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==============================================================================
UNIX Computer Security Checklist (Version 1.1)       Last Update   19-Dec-1995
==============================================================================
The Australian Computer Emergency Response Team has developed a checklist which
assists in removing common and known security vulnerabilities under the UNIX
Operating System.  It is based around recently discovered security
vulnerabilities and other checklists which are readily available (see 
references in Appendix C). 

This document can be retrieved via anonymous ftp from:
   ftp://ftp.auscert.org.au/pub/auscert/papers/unix_security_checklist

For information about detecting or recovering from an intrusion, see the
CERT security information document which can be retrieved via anonymous ftp
from:
   ftp://ftp.auscert.org.au/pub/cert/tech_tips/security_info

It is AUSCERT's intention to continue to update this checklist.  Any
comments should be directed via email to auscert@auscert.org.au.  Before
using this document, ensure you have the latest version.  New versions of this
checklist will be placed in the same area on the ftp server and should be 
checked for periodically. 

In order to make effective use of this checklist, readers will need to have 
a good grasp of basic UNIX system administration concepts.  Refer to C.9 and 
C.10 for books on UNIX system administration.

If possible, apply this checklist to a system before attaching it to a network.

In addition, we recommend that you use the checklist on a regular basis as well
as after you install any patches or new versions of the operating system, with
consideration given to the appropriateness of each action to your particular
situation. 

Command examples have been supplied for BSD-like and SVR4-like systems (see
Appendix F for operating system details and Appendix G for command details). 
Full directory paths and program options may vary for different flavours of
UNIX. If in doubt, consult your vendor documentation. 

For ease of use, the checklist has been organised into separate, logically
cohesive sections.  All sections are important.  An abbreviated version of
this checklist can be found in Appendix D. 

CHECKLIST INDEX:        1.0  Patches
                        2.0  Network security
                        3.0  ftpd and anonymous ftp
                        4.0  Password and account security
                        5.0  File system security
                        6.0  Vendor operating system specific security
                        7.0  Security and the X Window System
    
APPENDICES:      Appendix A  Other AUSCERT information sources
                 Appendix B  Useful security tools
                 Appendix C  References
                 Appendix D  Abbreviated Checklist
                 Appendix E  Shell Scripts
                 Appendix F  Table of operating systems by flavour
                 Appendix G  List of commands by flavour

Any trademarks which appear in this document are registered to their
respective owners.

==============================================================================
1.0  Patches 
==============================================================================
   *    Retrieve the latest patch list from your vendor and install any 
        patches not yet installed that are recommended for your system.
            Some patches may re-enable default configurations.  For this 
            reason, it is important to go through this checklist AFTER
            installing ANY new patches or packages.
   *    Details on obtaining patches may be found in Section 6.
   *    Verify the digital signature of any signed files.  Tools like PGP may 
        be used to sign files and to verify those signatures.
        (Refer to B.15 for PGP access information).
   *    If no digital signature is supplied but an md5(1) checksum is supplied,
        then verify the checksum information to confirm that you have retrieved 
        a valid copy.
        (Refer to B.10 for MD5 access information).
   *    If only a generic sum(1) checksum is provided, then check that.  Be
        aware that the sum(1) checksum should not be considered secure.

==============================================================================
2.0  Network security
==============================================================================
        The following is a list of features that can be used to help
        prevent attacks from external sources.

 2.1  Filtering
   *    ENSURE that ONLY those services which are required from outside your 
        domain are allowed through your router filters.
            In particular, if the following are not required outside your
            domain, then filter them out at the router.

             NAME     PORT  PROTOCOL            NAME    PORT  PROTOCOL

             echo     7     TCP/UDP             login   513   TCP
             systat   11    TCP                 shell   514   TCP
             netstat  15    TCP                 printer 515   TCP
             bootp    67    UDP                 biff    512   UDP
             tftp     69    UDP                 who     513   UDP
             link     87    TCP                 syslog  514   UDP
             supdup   95    TCP                 uucp    540   TCP
             sunrpc   111   TCP/UDP             route   520   UDP
             NeWS     144   TCP                 openwin 2000  TCP
             snmp     161   UDP                 NFS     2049  UDP/TCP
             xdmcp    177   UDP                 X11     6000 to 6000+n TCP
             exec     512   TCP                 (where n is the maximum number
                                                 of X servers you will have)

        Note: Any UDP service that replies to an incoming packet may be 
              subject to a denial of service attack.

        See CERT advisory CA-95.01 (C.8) for more details.

        Filtering is difficult to implement correctly.  For information on
        packet filtering, please see Firewalls and Internet Security (C.6)
        and Building Internet Firewalls (C.7).

 2.2  "r" commands

  2.2.1 If you don't NEED to use the "r" commands...
   *    DO disable all "r" commands (rlogin, rsh etc.) unless specifically 
        required.
            This may increase your risk of password exposure in network
            sniffer attacks, but "r" commands have been a regular source of 
            insecurities and attacks.  Disabling them is by far the lesser of 
            the two evils (see 2.9.1).

  2.2.2 If you must run the "r" commands...
   *    DO use more secure versions of the "r" commands for cases where 
        there is a specific need.
            Wietse Venema's logdaemon package contains a more secure version
            of the "r" command daemons.  These versions can be configured to 
            consult only /etc/hosts.equiv and not $HOME/.rhosts.  There is 
            also an option to disable the use of wildcards ('+').
        Refer to B.13 for access information for the logdaemon package
   *    DO filter ports 512,513 and 514 (TCP) at the router if you do use any
        of the "r" commands.
            This will stop people outside your domain from exploiting these
            commands but will not stop people inside your domain.
            To do this you will need to disable these commands (see 2.2.1).
   *    DO use tcp_wrappers to provide greater access and logging on these
        network services (see 2.12).

 2.3  /etc/hosts.equiv

  2.3.1 It is recommended that the following action be taken whether or not 
        the "r" commands are in use on your system.
     *    CHECK if the file /etc/hosts.equiv is required.   
              If you are running "r" commands, this file allows other hosts to 
              be trusted by your system.  Programs such as rlogin can then be 
              used to log on to the same account name on your machine from a 
              trusted machine without supplying a password.
              If you are not running "r" commands or you do not wish to 
              explicitly trust other systems, you should have no use for
              this file and it should be removed.  If it does not exist, it 
              cannot cause you any problems if any of the "r" commands are 
              accidentally re-enabled.

  2.3.2 If you must have a /etc/hosts.equiv file
     *    ENSURE that you keep only a small number of TRUSTED hosts listed. 
     *    DO use netgroups for easier management if you run NIS (also known 
          as YP) or NIS+.
     *    DO only trust hosts within your domain or under your management.
     *    ENSURE that you use fully qualified hostnames, 
              i.e., hostname.domainname.au
     *    ENSURE that you do NOT have a '+' entry by itself anywhere in the
          file as this may allow any user access to the system.
     *    ENSURE that you do not use '!' or '#' in this file.
              There is no comment character for this file.
     *    ENSURE that the first character of the file is not '-'.  
          Refer to the CERT advisory CA-91:12 (C.8).
     *    ENSURE that the permissions are set to 600.
     *    ENSURE that the owner is set to root.
     *    CHECK it again after each patch or operating system installation.

 2.4  /etc/netgroup
   *    If you are using NIS (YP) or NIS+, DO define each netgroup to contain 
        only usernames or only hostnames.
            All utilities parse /etc/netgroup for either hosts or
            usernames, but never both.  Using separate netgroups makes it
            easier to remember the function of each netgroup. The added
            time required to administer these extra netgroups is a small
            cost in ensuring that strange permission combinations have not
            left your machine in an insecure state.
            Refer to the manual pages for more information.

 2.5  $HOME/.rhosts

  2.5.1 It is recommended that the following action be taken whether or not 
        the "r" commands are in use on your system.
      *     ENSURE that no user has a .rhosts file in their home directory.
               They pose a greater security risk than /etc/hosts.equiv, as one
               can be created by each user.  There are some genuine needs for
               these files, so hear each one on a case-by-case basis; e.g.,
               running backups over a network unattended.
      *     DO use cron to periodically check for, report the contents of 
            and delete $HOME/.rhosts files.  Users should be made aware that 
            you regularly perform this type of audit, as directed by policy.

   2.5.2 If you must have such a file
      *    ENSURE the first character of the file is not '-'.  
           Refer to the CERT advisory CA-91:12 (C.8).
      *    ENSURE that the permissions are set to 600.
      *    ENSURE that the owner of the file is the account's owner.
      *    ENSURE that the file does NOT contain the symbol "+" on any line as
           this may allow any user access to this account.
      *    ENSURE that usage of netgroups within .rhosts does not allow
           unintended access to this account.
      *    ENSURE that you do not use '!' or '#' in this file.
              There is no comment character for this file.
      *    REMEMBER that you can also use logdaemon to restrict the use of
           $HOME/.rhosts (see 2.2.2).

 2.6  NFS
      When using NFS, you implicitly trust the security of the NFS server
      to maintain the integrity of the mounted files.
   *    DO filter NFS traffic at the router.
            Filter TCP/UDP on port 111 
                   TCP/UDP on port 2049 
            This will prevent machines not on your subnet from accessing
            file systems exported by your machines.
   *    DO apply all available patches.
            NFS has had a number of security vulnerabilities.
   *    DO disable NFS if you do not need it.
            See your vendor supplied documentation for detailed instructions.
   *    DO enable NFS port monitoring.
            Calls to mount a file system will then be accepted from ports < 1024
            only. This will provide added security in some circumstances.
            See your vendor's documentation to determine whether this is an 
            option for your version of UNIX (see also 6.1.8 and 6.2.4).
   *    DO use /etc/exports or /etc/dfs/dfstab to export ONLY the file systems 
        you need to export. 
            If you aren't certain that a file system needs to be exported, 
            then it probably shouldn't be exported.
   *    DO NOT self-reference an NFS server in its own exports file.
            i.e., The exports file should not export the NFS server to
            itself in part or in total.  In particular, ensure the NFS server 
            is not contained in any netgroups listed in its exports file. 
   *    DO NOT allow the exports file to contain a 'localhost' entry.
   *    DO export to fully qualified hostnames only.
            i.e., Use the full machine address 'machinename.domainname.au' and
            do not abbreviate it to 'machinename'.
   *    ENSURE that export lists do not exceed 256 characters.
            If you have access lists of hosts within /etc/exports, the list 
            should not exceed 256 characters AFTER any host name aliases have 
            been expanded.
            Refer to the CERT Advisory CA-94:02 (C.8).
   *    DO run fsirand for all your file systems and rerun it periodically.
            Firstly, ensure that you have installed any patches for fsirand.
            Then ensure the file system is unmounted and run fsirand. 
            Predictable file handles assist crackers in abusing NFS. 
   *    ENSURE that you never export file systems unintentionally to the world.
            Use a -access=host.domainname.au option or equivalent in 
            /etc/exports. 
            See the manual page for "exports" or "dfstab" for further examples.
   *    DO export file systems read-only (-ro) whenever possible.  
            See the manual page for "exports" or "dfstab" for more information.
   *    If NIS is required in your situation, then DO use the secure option in
        the exports file and mount requests (if the secure option is available).
   *    DO use showmount -e to see what you currently have exported.
   *    ENSURE that the permissions of /etc/exports are set to 644.
   *    ENSURE that /etc/exports is owned by root.  
   *    ENSURE that you run a portmapper or rpcbind that does not forward 
        mount requests from clients.
            A malicious NFS client can ask the server's portmapper daemon 
            to forward requests to the mount daemon.  The mount daemon 
            processes the request as if it came directly from the portmapper.
            If the file system is self-mounted this gives the client 
            unauthorised permissions to the file system.
            Refer to section B.14 for how to obtain an alternate portmapper or
            rpcbind that disallow proxy access.
            Refer to the CERT Advisory 94:15 (C.8).
   *    REMEMBER that changes in /etc/exports will take effect only after
        you run /usr/etc/exportfs or equivalent. 

   Note: A "web of trust" is created between hosts connected to each other via
         NFS.  That is, you are trusting the security of any NFS server you use.
 
 2.7  /etc/hosts.lpd
   *    ENSURE that the first character of the file is not '-'.  
        (Refer to the CERT advisory CA-91:12 (see C.8)).
   *    ENSURE that the permissions on this file are set to 600.
   *    ENSURE that the owner is set to root.
   *    ENSURE that you do not use '!' or '#' in this file.
            There is no comment character for this file.

 2.8  Secure terminals
   *    This file may be called /etc/ttys, /etc/default/login or
        /etc/security.  See the manual pages for file format and usage 
        information.
   *    ENSURE that the secure option is removed from all entries that 
        don't need root login capabilities. 
            The secure option should be removed from console if you do not 
            want users to be able to reboot in single user mode.
            Note: This does not affect usability of the su(1) command.
   *    ENSURE that this file is owned by root.
   *    ENSURE that the permissions on this file are 644.

 2.9  Network services

  2.9.1  /etc/inetd.conf
    *    ENSURE that the permissions on this file are set to 600.
    *    ENSURE that the owner is root.
    *    DO disable any services which you do not require. 
            - To do this we suggest that you comment out ALL services by 
              placing a "#" at the beginning of each line.  Then enable 
              the ones you NEED by removing the "#" from the beginning 
              of the line.  In particular, it is best to avoid "r" commands 
              and tftp, as they have been major sources of insecurities.  
            - For changes to take effect, you need to restart the inetd 
              process.  Do this by issuing the commands in G.1.  For some 
              systems (including AIX), these commands are not sufficient.
              Refer to vendor documentation for more information.

  2.9.2  Portmapper
    *    DO disable any non-required services that are started up in the system 
         startup procedures and register with the portmapper.  See G.2 for a 
         command to help check for registered services.

 2.10  Trivial ftp (tftp)
   *    If tftp is not needed, comment it out from the file 
        /etc/inetd.conf and restart the inetd process (as above).
   *    If required, read the AUSCERT Advisory SA-93:05 (see A.1) and follow 
        the recommendations.

 2.11  /etc/services
   *    ENSURE that the permissions on this file are set to 644.
   *    ENSURE that the owner is root.

 2.12  tcp_wrapper (also known as log_tcp)
   *    ENSURE that you are using this package.
            - Customise and install it for your system.
            - Enable PARANOID mode
            - Consider running with the RFC931 option
            - Deny all hosts by putting "all:all" in /etc/hosts.deny and
              explicitly list trusted hosts who are allowed access to your
              machine in /etc/hosts.allow.
            - See the documentation supplied with this package for details 
              about how to do the above.
   *    DO wrap all TCP services that you have enabled in /etc/inetd.conf
   *    DO consider wrapping any udp services you have enabled.  If you
        wrap them, then you will have to use the nowait option in the 
        /etc/inetd.conf file.
   *    See section B.4 for instructions to obtain tcp_wrapper.

 2.13  /etc/aliases
   *    Comment out the "decode" alias by placing a "#" at the beginning
        of the line.  For this change to take effect you will need to run
        /usr/bin/newaliases.  If you run NIS (YP), you will then need to 
        rebuild your maps (see G.3).
   *    ENSURE that all programs executable by an alias are owned by root,
        have permissions 755 and are stored in a systems directory 
        e.g., /usr/local/bin.  If smrsh is in use, program execution may be
        further restricted.  Refer to the smrsh documentation for more details 
        (see B.9).

 2.14  Sendmail
   *    DO use the latest version of Eric Allman's sendmail 8.x (currently
        8.7.3), as it currently contains no KNOWN vulnerabilities.  
            The latest version is available via anonymous FTP from: 
               ftp://ftp.auscert.org.au/pub/mirrors/ftp.cs.berkeley.edu
                        /ucb/sendmail
            NOTE: If you don't already run Eric Allman's sendmail.8.7.*,
                  then it may take you some time to build, install, and 
                  configure the system to your needs.  Other sendmail(8) 
                  configuration files may not be compatible with 
                  sendmail(8) 8.7.x.  There is some help available for 
                  converting from SUN's sendmail: bundled with the distribution
                  of sendmail(8) v8.7.x is a document on converting standard 
                  SUN configuration files to sendmail(8) v8.*.  This is located
                  in the distribution, in the file:
                      contrib/converting.sun.configs 
   *    If you use a vendor version of sendmail, ENSURE that you have 
        installed the latest patches as sendmail(8) has been a source of a 
        number of security vulnerabilities.
            Refer to AUSCERT Advisories SA-93:10, AA-95.08 and AA-95.09b (A.1) 
            and CERT Advisories CA-94:12, CA-95:05 and CA-95:08 (C.8).
   *    If you require progmailer functionality then DO use smrsh (see B.9).
   *    If you do not require progmailer functionality then DO disable mail to
        programs by setting this field to /bin/false in the sendmail 
        configuration file.
   *    ENSURE that your version of sendmail does not have the wizard
        password enabled (see G.4).  ENSURE that if you have a line starting 
        with "OW" in /etc/sendmail.cf, it only has a "*" next to it.
   *    DO increase sendmail(8) logging to a minimum log level of 9. 
            This will help detect attempted exploitation of the sendmail(8)
            vulnerabilities.  See G.5 for example commands.
   *    DO increase the level of logging provided by syslog.
            Enable a minimum level of "info" for mail messages to be
            logged to the console and/or the syslog file.  See G.6 for 
            example code and instructions.
   *    REMEMBER that you will need to restart sendmail for any changes to take
        effect.  If you are running a frozen configuration file (sendmail.fc),
        you will need to rebuild it before restarting sendmail(8) (see G.7).

 2.15  majordomo
   *    ENSURE that your version is greater than 1.91.
        See AUSCERT Advisory SA-94.03 (see A.1) for more details.

 2.16  fingerd
   *    If your version of fingerd is older than than 5 November 1988, DO
        replace it with a newer version.
   *    Finger can provide a would-be intruder with a lot of information
        about your host.  CONSIDER the finger information you provide and
        think about reducing the content by disabling finger or by
        replacing it with a version that only offers restricted information.
        NOTE:  other services such as rusers and netstat may give out similar
               information.
   *    DO NOT use GNU finger v1.37 as it may allow intruders to read any file. 

 2.17  UUCP
   *    DO disable the uucp account, including the shell that it executes 
        for logging in, if it is not used at your site.
            uucp may be shipped in a dangerous state.   
   *    REMOVE any .rhosts file at the uucp home directory.
   *    ENSURE that the file L.cmds is owned by root.
   *    ENSURE that no uucp owned files or directories are world writable.
   *    ENSURE that you have assigned a different uucp login for each site
        that needs uucp access to your machine.  
   *    ENSURE that you have limited the number of commands that each uucp 
        login can execute to a bare minimum. 
   *    DO consider deleting the whole uucp subsystem if it is not required.
   *    ENSURE there are no vendor-supplied uucp or root crontab entries.

 2.18  REXD
   *   DO disable this service.  
           Comment this out in the inetd.conf file.  See section 2.9.1 for
           details on how to do this.  rexd servers have little or no 
           security in their design or implementation.  Intruders can exploit 
           this service to execute commands as any user.

 2.19  World Wide Web (WWW) - httpd
   *   ENSURE that you are using the most recent version of the http daemon 
       of your choice.
   *   DO run the server daemon httpd as a specially created nonprivileged 
       user such as 'httpd'.
           This way, if an intruder finds a vulnerability in the server 
           they will only have access privileges for this unprivileged user.
   *   DO NOT run the server daemon as root.
   *   DO NOT run the client processes as root.
   *   DO run httpd in a chroot(1) environment.
           This sets up an alternate root directory that severely limits
           access of http clients to the rest of the disk.
   *   For systems which do not have a chroot(1) command, use of chrootuid
       (see B.16) may be of assistance.
   *   DO carefully go through the configuration options for your server.
   *   DO use the configuration options to give extra protection to
       sensitive directories by turning off the 'include files' feature.
           This will disallow files from these directories from being
           included in HTML documents.
   *   DO use CGIWRAP.  (See B.17)
   *   DO NOT run CGI (Common Gateway Interface) scripts if they are not 
       required.
   *   DO be very careful in constructing CGI programs.  
            These programs compute information to be returned to clients
            and are often driven by input from the remote user who may be
            hostile.  If these programs are not carefully constructed, it may 
            be possible for remote users to subvert them to execute arbitrary 
            commands on the server system.  Almost all vulnerabilities arise 
            from these issues.
   *   DO provide CGIs as statically linked binaries rather than as interpreted
       scripts.
            This will remove the need for a command interpreter to be   
            available inside the chrooted environment.
   *   ENSURE that the contents, permissions and ownership of files in the 
       cgi-bin directory are what you expect them to be (see your site security
       policy document for more details).
   *   AVOID passing user input directly to command interpreters
       such as Perl, AWK, UNIX shells or programs that allow commands 
       to be embedded in outgoing messages such as /usr/ucb/mail
   *   FILTER user input for potentially dangerous characters before 
       it is passed to any command interpreters. 
             Possibly dangerous characters include \n \r (.,/;~!)>|^&$`< .
             (Refer to the CERT Advisory CA-95:04 (see C.8)).

==============================================================================
3.0  ftpd and anonymous ftp
==============================================================================
 3.1  Versions
   *    ENSURE that you are using the most recent version of the ftp daemon 
        of your choice.
   *    DO consider installing the Washington University ftpd if you don't 
        already have it (see B.19).
   *    For BSDI systems, patch 005 should be applied to version 1.1 of the
        BSD/386 software (see B.20).

 3.2  Configuration 
   *    CHECK all default configuration options on your ftp server.
   *    ENSURE that your ftp server does not have the SITE EXEC command
        (see G.8 for command details).
   *    ENSURE that you have set up a file /etc/ftpusers which specifies
        those users that are NOT allowed to connect to your ftpd.  
            This should include, as a MINIMUM, the entries: root, bin,
            uucp, ingres, daemon, news, nobody and ALL vendor supplied 
            accounts.

 3.3  Anonymous ftp only
   *    To ascertain whether you are running anonymous ftp, try to connect
        to the localhost using anonymous ftp.  Be sure to give an RFC822
        compliant username as the password (see G.9).
   *    To disable anonymous ftp, move or delete all files in ~ftp/ and then 
        remove the user ftp from your password file.        
   *    If you are running distributed passwords (e.g., NIS, NIS+) then you
        will need to check the password entries served to your machine as
        well as those in your local password file.

  3.3.1  Configuration of your ftp server
    *    CHECK all default configuration options on your ftp server.
             Not all versions of ftp are configurable.  If you have a 
             configurable version of ftp (e.g., wu-ftp) then make sure that     
             all delete, overwrite, rename, chmod and umask options (there
             may be others) are NOT allowed for guests and anonymous users. 
             In general, anonymous users should not have any unnecessary 
             privileges.
    *    ENSURE that you DO NOT include a command interpreter (such as a shell 
         or tools like perl) in ~ftp/bin, ~ftp/usr/bin, ~ftp/sbin or similar 
         directory configurations that can be executed by SITE EXEC
         (Refer to AUSCERT advisory SA-94.01 (see A.1)).
    *    DO NOT keep system commands in ~ftp/bin, ~ftp/usr/bin, ~ftp/sbin 
         or similar directory configurations that can be executed by SITE EXEC.
            It may be necessary to keep some commands, such as uncompress, in
            these locations.  Consider the inclusion of each command on a case
            by case basis and be aware that the presence of such commands may 
            make it possible for local users to gain unauthorised access.
            Be wary of including commands that can execute arbitrary commands.
            For example, some versions of tar may allow you to execute an
            arbitrary file.
            (Refer to AUSCERT advisory SA-94.01 (see A.1)).
    *    ENSURE that you use an invalid password and user shell for the ftp
         entry in the system password file and the shadow password file (if
         you have one). It should look something like:
            ftp:*:400:400:Anonymous FTP:/home/ftp:/bin/false
         where /home/ftp is the anonymous ftp area.
    *    ENSURE that the permissions of the ftp home directory (~ftp/) are set
         to 555 (read nowrite execute), owner set to root (NOT ftp).
    *    ENSURE that you DO NOT have a copy of your real /etc/passwd file
         as ~ftp/etc/passwd.  
            Create one from scratch with permissions 444, owned by root.  It 
            should not contain the names of any accounts in your real 
            password file.  It should contain only root and ftp.  These 
            should be dummy entries with disabled passwords eg:
               root:*:0:0:Ftp maintainer::  
               ftp:*:400:400:Anonymous ftp::
         The password file is used only to provide uid to username mapping for
         ls(1) listings.
    *    ENSURE that you DO NOT have a copy of your real /etc/group file as 
         ~ftp/etc/group. 
            Create one from scratch with permissions 444, owned by root.  
    *    ENSURE the files ~ftp/.rhosts and ~ftp/.forward do not exist.
    *    DO set the login shell of the ftp account to a non-functional shell
         such as /bin/false.

  3.3.2  Permissions
    *    ENSURE NO files or directories are owned by the ftp account or have 
         the same group as the ftp account. 
            If they are, it may be possible for an intruder to replace them 
            with a trojan version.
    *    ENSURE that the anonymous ftp user cannot create files or directories
         in ANY directory unless required (see Section 3.3.3).
    *    ENSURE that the anonymous ftp user can only read information in public
         areas.
    *    ENSURE that the permissions of the ftp home directory (~ftp/) are set
         to 555 (read nowrite execute), owner set to root (NOT ftp).
    *    ENSURE that the system subdirectories ~ftp/etc and ~ftp/bin 
         have the permissions 111 only, owner set to root.
    *    ENSURE that the permissions of files in ~ftp/bin/* have the
         permissions 111 only, owner set to root.
    *    ENSURE that the permissions of files in ~ftp/etc/* are set to
         444, owner set to root.
    *    ENSURE that there is a mail alias for ftp to avoid mail bounces.
    *    ENSURE /usr/spool/mail/ftp is owned by root with permissions 400.

  3.3.3  Writable directories
    *    ENSURE that you don't have any writable directories. 
            It is safest not to have any writable directories. If you do 
            have any, we recommend that you limit the number to one.    
    *    ENSURE that writable directories are not also readable.
            Directories that are both writable and readable may be used  
            in an unauthorised manner. 
    *    ENSURE that any writable directories are owned by root and have 
         permissions 1733.  
    *    DO put writable directories on a separate partition if possible. 
            This will help to prevent denial of service attacks. 
    *    DO read Anonymous FTP Configuration Guidelines (see B.21).

  3.3.4  Disk mounting
    *    NEVER mount disks from other machines to the ~ftp hierarchy 
         unless they are set read-only in the mount command.  

==============================================================================
4.0  Password and account security
==============================================================================
        This section of the checklist can be incorporated as part of a 
        password and account usage policy.

 4.1  Policy
   *    ENSURE that you have a password policy for your site. 
            See the AUSCERT Advisory SA-93.04 (see A.1).
   *    ENSURE you have a User Registration Form for each user on each 
        system.  Make sure that this form includes a section that the 
        intending applicant signs, stating that they have read your account
        usage policy and what the consequences are if they misuse their 
        account.

 4.2  Proactive Checking
   *    DO use anlpasswd to proactively screen passwords as they are entered.
            This program runs a series of checks on passwords when they are
            set, which assists in avoiding poor passwords.  It works with
            normal, shadow and NIS (or yp) password systems. 
            (Refer to section B.3 for how to obtain it).
   *    DO check passwords periodically with Crack. 
            (Refer to section B.1 for how to obtain Crack).
   *    DO apply password ageing (if possible).

 4.3  NIS, NIS+ and /etc/passwd entries
   *    DO NOT run NIS or NIS+ if you don't really need it.
   *    If NIS functionality is required, DO use NIS+ if possible.
   *    ENSURE that the only machines that have a '+' entry in the /etc/passwd
        files are NIS (YP) clients; i.e., NOT the NIS master server!
            There appears to be conflicting documentation and
            implementations regarding the '+' entry format and so a
            generic solution is not available here.  It would be best to
            consult your vendor's documentation.
            Some of the available documentation suggests placing a '*' in
            the password field, which is NOT consistent across all
            implementations of NIS.  We recommend testing your systems on a
            case-by-case basis to see if they correctly implement the '*'
            in the password field.
            See G.10 for instructions.
   *    ENSURE that /etc/rc.local or the equivalent startup procedure is set up
        to start ypbind with the -s option.
            This may not be applicable on all systems.  Check your 
            documentation.
   *    DO use secure RPC.

 4.4  Password shadowing 
   *    DO enable vendor supplied password shadowing or a third party 
        product.
            Password shadowing restricts access to users' encrypted passwords.
   *    DO periodically audit your password and shadow password files 
        for unauthorised additions or inconsistencies.

 4.5  Administration
   *    ENSURE that you regularly audit your system for dormant accounts
        and disable any that have not been used for a specified period,
        say 3 months.  Send out account renewal notices by post and delete 
        any accounts of users that do not reply.
        [NOTE: Do not email renewal notices because any accounts being used
        illegitimately will reply as expected and hence will not be discovered]
   *    ENSURE that all accounts have passwords.  Check shadow or NIS passwords 
        too, if you have them.
        i.e., the password field is not empty.
   *    ENSURE that any user area is adequately backed up and archived.
   *    DO regularly monitor logs for successful and unsuccessful su(1) 
        attempts.
   *    DO regularly check for repeated login failures.
   *    DO regularly check for LOGIN REFUSED messages.
   *    Consider quotas on user accounts if you do not have them.
   *    Consider requiring that users physically identify themselves before
        granting any requests regarding accounts (e.g., before creating a
        user account).

 4.6  Special accounts
   *    ENSURE that there are no shared accounts other than root in accordance
        with site security policy. 
            i.e., more than one person should not know the password to an
            account.
   *    Disable guest accounts.  
            Better yet, do not create guest accounts!
            [NOTE: Some systems come preconfigured with guest accounts]
   *    DO use special groups (such as the "wheel" group under SunOS) to
        restrict which users can use su to become root.
   *    DISABLE ALL default vendor accounts shipped with the Operating System.  
            This should be checked after each upgrade or installation.
   *    DO Disable accounts that have no password which execute a command, for
        example "sync".
            Delete or change ownership of any files owned by these
            accounts.  Ensure that these accounts do not have any cron or
            at jobs. It is best to remove these accounts entirely.
   *    DO assign non-functional shells (such as /bin/false) to system
        accounts such as bin and daemon and to the sync account if it is
        not needed.
   *    DO put system accounts in the /etc/ftpusers file so they cannot use 
        ftp.
            This should include, as a MINIMUM, the entries: root, bin,
            uucp, ingres, daemon, news, nobody and ALL vendor supplied 
            accounts.

 4.7  Root account
   *    DO restrict the number of people who know the root password.
            These should be the same users registered with groupid 0
            (e.g., wheel group on SunOS).  Typically this is limited to at most
            3 or 4 people.  
   *    DO NOT log in as root over the network, in accordance with site
        security policy.
   *    DO su from user accounts rather than logging in as root.  
            This provides greater accountability.
   *    ENSURE root does not have a ~/.rhosts file.
   *    ENSURE "." is not in root's search path.
   *    ENSURE root's login files do not source any other files not
        owned by root or which are group or world writable.
   *    ENSURE root cron job files do not source any other files not
        owned by root or which are group or world writable.
   *    DO use absolute path names when root. 
            e.g., /bin/su, /bin/find, /bin/passwd.  This is to stop the
            possibility of root accidentally executing a trojan horse.  To
            execute commands in the current directory, root should prefix
            the command with "./", e.g., ./command.

 4.8  .netrc files
   *    DO NOT use .netrc files unless it is absolutely necessary.
   *    If .netrc files must be used, DO NOT store password information in
        them.

 4.9  GCOS field
   *    DO include information in the GCOS field of the password file which
        can be used to identify your site if the password file is stolen.
        e.g.,  joe:*:10:10:Joe Bloggs, Organisation X:/home/joe:/bin/sh

==============================================================================
5.0  File system security
==============================================================================
 5.1  General
   *    ENSURE that there are no .exrc files on your system that have
        no legitimate purpose.
   *    DO consider using the EXINIT environment variable to disable .exrc
        file functionality.
            These files may inadvertently perform commands that may compromise
            the security of your system if you happen to start either vi(1) or
            ex(1) in a directory which contains such a file.  
        See G.11 for example commands to find .exrc files.
   *    ENSURE that any .forward files in user home directories do not 
        execute an unauthorised command or program.
            The mailer may be fooled into allowing a normal user privileged 
            access.  Authorised programs may be restricted through use of 
            smrsh (see B.9).
        See G.12 for example commands to find .forward files.
        (Refer to AUSCERT Advisory SA-93.10 (see A.1)).
 
 5.2  Startup and shutdown scripts
   *    ENSURE startup and shutdown scripts do not chmod 666 motd.  
            This allows users to change system message for the day.
   *    ENSURE that the line "rm -f /tmp/t1" (or similar) exists in a startup 
        script to clean up the temporary file used to create /etc/motd.  This 
        should occur BEFORE the code to startup the local daemons.

 5.3  /usr/lib/expreserve
   *    DO replace versions of /usr/lib/expreserve prior to July 1993 
        with a recommended patch from your vendor.  
            If this is not possible, then remove execute permission on
            /usr/lib/expreserve (see G.13).
            This will mean that users who edit their files with either vi(1)
            or ex(1) and have their sessions interrupted, will not be able to
            recover their lost work.  If you implement the above
            workaround, please advise your users to regularly save their
            editing sessions.
            (Refer to the CERT advisory CA-93:09 for advice on fixing this
            problem for the SunOS and Solaris environments).

 5.4  External file systems/devices
   *    DO mount file systems non-setuid and read-only where practical.
        (Refer to section 2.6)

 5.5  File Permissions 
   *    ENSURE that the permissions of /etc/utmp are set to 644.
   *    ENSURE that the permissions of /etc/sm and /etc/sm.bak are set to 2755.
   *    ENSURE that the permissions of /etc/state are set to 644.
   *    ENSURE that the permissions of /etc/motd and /etc/mtab are set to 644.
   *    ENSURE that the permissions of /etc/syslog.pid are set to 644.
            [NOTE: this may be reset each time you restart syslog.]
   *    DO consider removing read access to files that users do not need to 
        access.
   *    ENSURE that the kernel (e.g., /vmunix) is owned by root, has group set 
        to 0 (wheel on SunOS) and permissions set to 644.
   *    ENSURE that /etc, /usr/etc, /bin, /usr/bin, /sbin, /usr/sbin, /tmp and 
        /var/tmp are owned by root and that the sticky-bit is set on /tmp and on
        /var/tmp (see G.14).  Refer to the AUSCERT Advisory AA-95:05 (see A.1).
   *    ENSURE that there are no unexpected world writable files or 
        directories on your system.  
        See G.15 for example commands to find group and world writable files
        and directories.                           
   *    CHECK that files which have the SUID or SGID bit enabled, should have
        it enabled (see G.16).
   *    ENSURE the umask value for each user is set to something sensible 
        like 027 or 077. 
        (Refer to section E.1 for a shell script to check this).
   *    ENSURE all files in /dev are special files.
            Special files are identified with a letter in the first position of
            the permissions bits.  See G.17 for a command to find files in 
            /dev which are not special files or directories.
            Note: Some systems have directories and a shell script in /dev which
            may be legitimate.  Please check the manual pages for more 
            information.
   *    ENSURE that there are no unexpected special files outside /dev.
        See G.18 for a command to find any block special or character
        special files.

 5.6  Files run by root
        AUSCERT recommends that anything run by root should be owned by
        root, should not be world or group writable and should be located 
        in a directory where every directory in the path is owned by root 
        and is not group or world writable.
   *    CHECK the contents of the following files for the root account.
            Any programs or scripts referenced in these files should meet
            the above requirements:
            -  ~/.login, ~/.profile and similar login initialisation files
            -  ~/.exrc and similar program initialisation files
            -  ~/.logout and similar session cleanup files
            -  crontab and at entries
            -  files on NFS partitions 
            -  /etc/rc* and similar system startup and shutdown files
   *    If any programs or scripts referenced in these files source further 
        programs or scripts they also need to be verified.

 5.7  Bin ownership
        Many systems ship files and directories owned by bin (or sys).  This 
        varies from system to system and may have serious security implications.
   *    CHANGE all non-setuid files and all non-setgid files and directories 
        that are world readable but not world or group writable and that are 
        owned by bin to ownership of root, with group id 0 (wheel group under 
        SunOS 4.1.x).
            - Please note that under Solaris 2.x changing ownership of system 
              files can cause warning messages during installation of patches 
              and system packages.
            - Anything else should be verified with the vendor.

 5.8  Tiger/COPS
   *    Do run one or both of these.                         
            Many of the checks in this section can be automated by using
            these programs. 
   *    To obtain these programs, see B.2.

 5.9  Tripwire
   *    DO run statically linked binary
   *    DO store the binary, the database and the configuration file on 
        hardware write-protected media.
   *    To obtain this program, see B.5.

==============================================================================
6.0  Vendor operating system specific security
==============================================================================
        The following is a list of security issues that relate to specific
        UNIX operating systems.  This is not necessarily a complete list
        of available UNIX types or of problems for those that are listed.

 6.1  SunOS 4.1.x

  6.1.1 Patches
    * DO regularly ask your vendor for a complete list of patches.  Sun
      regularly updates a list of recommended and security patches, which 
      is available from:
            ftp://ftp.auscert.org.au/pub/mirrors/sunsolve1.sun.com/*
        or
            ftp://sunsolve1.sun.com/pub/patches/*

  6.1.2 IP forwarding and source routing
    This is particularly relevant if you are using your SUN box as a bastion
    host or duel homed system.
    *    ENSURE IP forwarding is disabled.
            You will need the following line in the kernel configuration
            file: 
                options "IPFORWARDING=-1" 
            For information on how to customise a kernel, see the file: 
                /usr/sys/`arch`/conf/README
    *    DO also consider disabling source routing.
            Leaving source routing  enabled may allow unauthorised traffic
            through.  Unfortunately there is no official method or patch
            for turning source routing off.  There is however an
            unsupported patch.  It is available via anonymous ftp from
        ftp://ftp.auscert.org.au/pub/mirrors/ftp.greatcircle.com/v03.n153.Z

  6.1.3 Framebuffers  /dev/fb   
    If somebody can log in to your Sun workstation from a remote source, they 
    can read the contents of your Framebuffer, which is /dev/fb. Sun provides 
    a mechanism which allows the user logging in on the console to have 
    exclusive access to the Framebuffer, by using the file /etc/fbtab. 
    A sample /etc/fbtab file:
        #
        # File:         /etc/fbtab
        # Purpose:      Specifies that upon login  to  /dev/console,  the
        #               owner,  group  and permissions of all supported 
        #               devices, including the framebuffer, will be set to 
        #               the user's username, the user's group and 0600.
        # Comments:     SunOS specific.
        # Note:         You cannot use \ to continue a line.
        #
        # Format:
        # Device        Permission      Colon separated device list.
        #
        /dev/console    0600            /dev/fb
        /dev/console    0600            /dev/bwone0:/dev/bwtwo0
        /dev/console    0600            /dev/cgone0:/dev/cgtwo0:/dev/cgthree0
        /dev/console    0600            /dev/cgfour0:/dev/cgsix0:/dev/cgeight0
        /dev/console    0600            /dev/cgnine0:/dev/cgtwelve0
        #
        /dev/console    0600            /dev/kb:/dev/mouse
        /dev/console    0600            /dev/fd0c:/dev/rfd0c
    After the above file has been created, reboot your machine, or log out 
    fully, then log back in again.
    Read the man page for fbtab(5) for more information.
    *    The login replacement from Wietse Venema's logdaemon package 
         supports a similar feature.
         (Refer to B.13 for information on how to retrieve the logdaemon
             package)
             
  6.1.4 /usr/kvm/sys/*
    *    ENSURE all files and directories under /usr/kvm/sys/ are not
        writable by group.  
            In SunOS 4.1.4 the default mode is 2775 with group staff,
            allowing users in group staff to trojan the kernel.

  6.1.5 /usr/kvm/crash
    *    REMOVE setgid privileges on /usr/kvm/crash with the command:
                # /bin/chmod g-s /usr/kvm/crash
            A group of kmem allows users to read the virtual memory of a 
            running system.

  6.1.6 /dev/nit (Network Interface Tap)
    *    DO run the CERT tool cpm to check if your system is running in 
         promiscuous mode.
            For access details for cpm see B.6.
    *    DO disable the /dev/nit interface if you do not need to run in
         promiscuous mode.
          - For SunOS 4.x and Solbourne systems, the promiscuous interface 
            to the network can be eliminated by removing the /dev/nit
            capability from the kernel.  Once the procedure is complete, you
            may remove the device file /dev/nit since it is no longer 
            functional.
          - Apply "method 1" as outlined in the System and Network
            Administration manual, in the section, "Sun System
            Administration Procedures," Chapter 9, "Reconfiguring the
            System Kernel."  Excerpts from the method are reproduced below:
                  # cd /usr/kvm/sys/sun[3,3x,4,4c]/conf
                  # cp CONFIG_FILE SYS_NAME
            [NOTE: that at this step, you should replace the CONFIG_FILE
            with your system specific configuration file if one exists.]

                  # chmod +w SYS_NAME
                  # vi SYS_NAME
                  #
                  # The following are for streams NIT support.  NIT is used by
                  # etherfind, traffic, rarpd, and ndbootd.  As a rule of thumb,
                  # NIT is almost always needed on a server and almost never
                  # needed on a diskless client.
                  #
                  pseudo-device   snit            # streams NIT
                  pseudo-device   pf              # packet filter
                  pseudo-device   nbuf            # NIT buffering module

            [Comment out the 3 "pseudo-device" lines; save and exit the
            editor before proceeding.]

                  # config SYS_NAME
                  # cd ../SYS_NAME
                  # make
                  # mv /vmunix /vmunix.old
                  # cp vmunix /vmunix
                  # /etc/halt
                  > b                                          
           
            [This step will reboot the system with the new kernel.]
            [NOTE: that even after the new kernel is installed, you need to
            take care to ensure that the previous vmunix.old , or other
            kernel, is not used to reboot the system.]
         See CERT Advisory CA_94.01 (see C.8)             

  6.1.7 Loadable drivers option
    *    DO remove the option for loadable modules from the kernel.  
           This will mean that a rebuild of the kernel and a reboot will be 
           necessary in order to load any additional kernel modules and 
           intruders will be prevented from being able to load extra kernel 
           modules dynamically.  To remove this option, comment out the line
              options        VDDRV           # loadable modules
           from the kernel configuration file and re-compile the kernel.
           NOTE: Some software may expect to be able to load additional modules 
                 such as device drivers.
           NOTE: Even after the new kernel is installed, you need to take care 
                 to ensure that the previous vmunix.old , or other kernel, is 
                 not used to reboot the system.

  6.1.8 NFS port monitoring
    *    DO enable NFS port monitoring (see also section 2.6).
           Add the following commands to /etc/rc.local:
               /bin/echo "nfs_portmon/W1" | /bin/adb -w /vmunix /dev/kmem > \
                 /dev/null 2>&1
               rpc.mountd
            
 6.2  Solaris 2.x

  6.2.1 Patches
    *    DO regularly ask your vendor for a complete list of patches.  Sun
         regularly updates a list of recommended and security patches, which 
         is available from:
            ftp://ftp.auscert.org.au/pub/mirrors/sunsolve1.sun.com/*
          or
            ftp://sunsolve1.sun.com/pub/patches/*

  6.2.2 IP forwarding and source routing
    This is particularly relevant if you are using your SUN box as a bastion
    host or duel homed system.
    *    DO disable IP forwarding and source routing.
            To do this you will need to edit the file /etc/rc.2.d/S69.inet
            and set the options ip_forwarding and ip_ip_forward_src_routed
            to zero as illustrated below:
                ndd -set /dev/ip ip_forwarding 0
                ndd -set /dev/ip ip_ip_forward_src_routed 0
            For the changes to take effect you will then need to reboot.

  6.2.3 Framebuffers  /dev/fbs  
    *        Solaris versions 2.3 and above have a protection facility for
             framebuffers which is a superset of the functionality provided
             by /etc/fbtab in SunOS 4.1.x.  
    *        Under Solaris, /dev/fbs is a directory that contains links to
             the framebuffer devices.  The /etc/logindevperm file contains
             information that is used by login(1) and ttymon(1M) to change
             the owner, group, and permissions of devices upon logging into
             or out of a console device.  By default, this file contains
             lines for the keyboard, mouse, audio, and frame buffer devices.

             A sample /etc/logindevperm file:
             #
             # File:     /etc/logindevperm
             # Purpose:  Specifies that upon login to /dev/console, the
             #           owner, group and permissions of all supported 
             #           devices, including the framebuffer, will be set to 
             #          the user's username, the user's group and 0600.
             # Comments:        SunOS specific.
             # Note:    You cannot use \ to continue a line.
             #
             # Format:
             # Device    Permission     Colon separated device list.
             #
             /dev/console   0600        /dev/kbd:/dev/mouse
             /dev/console   0600        /dev/sound/*         # audio devices
             /dev/console   0600        /dev/fbs/*           # frame buffers
            
             Read the man page for logindevperm(4) for more information.

  6.2.4 NFS port monitoring
    *    DO enable NFS port monitoring.
            To do this add the following lines to /etc/system:
                 set nfs:nfs_portmon = 1
              or in Solaris version 2.5
                 set nfssrv:nfs_portmon = 1
    *   See also section 2.6.

 6.3  IRIX
   *    DO regularly ask your vendor for a complete list of patches.  
   *    Some IRIX patches are available via anonymous ftp from:
            ftp://ftp.auscert.org.au/pub/mirrors/ftp.sgi.com/security/*
          or
            ftp://ftp.auscert.org.au/pub/mirrors/sgigate.sgi.com/*
   *    DO read the FAQ on IRIX security.
            A copy can be obtained via anonymous ftp from
            ftp://ftp.auscert.org.au/pub/mirrors/ftp.uu.net/sgi/security.Z
   *    For systems which do not have the chroot(1) command, use of
        chrootuid (see B.16) may be of assistance.
   *    DO use the software tool rscan.  
            It checks for many common IRIX-specific security vulnerabilities 
            and problems. (Refer to B.11 for information on where to
            get a copy of rscan)

 6.4  AIX
   *    DO regularly ask your vendor for a complete list of patches.
   *    Some AIX patches are available via anonymous ftp from:
            ftp://ftp.auscert.org.au/pub/mirrors/software.watson.ibm.com
                        /aix-patches

 6.5  HP/UX
   *    DO regularly ask your vendor for a complete list of patches.  
        HP has set up an automatic server to allow patches and other security
        information to be retrieved via email.  Email should be sent to the
        address
                support@support.mayfield.hp.com.  
        The subject line of the message will be ignored. The body (text) of 
        the message should be of the format

                send XXXX

        where XXXX is the identifier for the information you want retrieved.  
        For example, to retrieve the patch PHSS_4834, the message would be 
                send PHSS_4834.
        To receive the HP SupportLine mail service user's guide 
                send guide.txt
        To receive the readme file for a patch 
                send doc PHSS_4834
        To receive the original HP bulletin 
                send doc HPSBUX9410-018.

        HP also has a World Wide Web server to browse and retrieve bulletins 
        and patches.  The URL is:
                http://support.mayfield.hp.com/

 6.6  OSF
   *    DO regularly ask your vendor for a complete list of patches.   
        Some patches are available from:
            ftp://ftp.auscert.org.au/pub/mirrors/ftp.service.digital.com
                        /osf/<v>/ssrt*
          or
            ftp://ftp.service.digital.com/pub/osf/<v>/ssrt*
        where <v> is the version of the operating system that you run.

 6.7  ULTRIX
   *    DO regularly ask your vendor for a complete list of patches.  
        Some patches are available from:
            ftp://ftp.auscert.org.au/pub/mirrors/ftp.service.digital.com
                        /ultrix/<p>/<v>/ssrt*
          or
            ftp://ftp.service.digital.com/pub/ultrix/<p>/<v>/ssrt*
        where <p> is either mips or vax; and
        where <v> is the version of the operating system that you run.

==============================================================================
7.0  Security and the X Window System
==============================================================================
        Access to your X server may be controlled through either a host-
        based or user-based method.  The former is left to the discretion
        of the Systems Administrator at your site and is useful as long as
        all hosts registered in the /etc/Xn.hosts file have users that can be
        trusted, where "n" represents your X server's number.

        This may not be possible at every site, so a better method is
        to educate each and every user about the security implications
        (see references below).  Better still, when setting up a user, give
        them a set of X security related template files, such as .xserverrc 
        and .xinitrc. These are located in the users home directory.

        You are strongly advised to read the section on X window system 
        security referred to in the X Window System Administrators Guide (C.4).

 7.1  Problems with xdm
        Note: Release 6 of X11 is now available and solves many problems
        associated with X security which were present in previous releases.  
        If possible, obtain the source for R6 and compile and install it on 
        your system.  See B.18 for how to retrieve the source for X11R6.
   *    xdm bypasses the normal getty and login functions, which means that 
        quotas for the user, ownership of /dev/console and possibly other
        preventive measures put in place by you may be ignored. 
   *    You should consult your vendor and ask about potential security holes
        in xdm and what fixes are available.
   *    If you are running a version of xdm earlier than October 1995 then 
        you should update to a newer version.
        (Refer to CERT Vendor-Initiated Bulletin VB-95:08, see C.8)

 7.2  X security - General
   *    DO Read the man pages for xauth and Xsecurity.
            Use this information to set up the security level you require.
   *    ENSURE that the permissions on /tmp are set to 1777 (or drwxrwxrwt).
            i.e., the sticky bit should be set.  The owner MUST always be
            root and group ownership should be set to group-id 0, which is
            "wheel" or "system".
            -  If the sticky bit is set, no one other than the owner can 
               delete the file /tmp/.X11-unix/X0, which is a socket for your 
               X server.  Once this file is deleted, your X server will no 
               longer be accessible.
            -  See G.14 for example commands to set the correct permissions 
               and ownership for /tmp.
    *   DO use the X magic cookie mechanism MIT-MAGIC-COOKIE-1 or better. 
            With logins under the control of xdm (see 7.1), you can turn on 
            authentication by editing the xdm-config file and setting  the
            DisplayManager*authorize attribute to true.  
            When granting access to the screen from another machine, use
            the xauth command in preference to the xhost command.
    *   DO not permit access from arbitrary hosts.
            Remove all instances of the 'xhost +' command from the
            system-wide  Xsession file, from user .xsession files, and from
            any application programs or shell scripts that use the X window
            system. 
            
==============================================================================
Appendix A:  Other AUSCERT information sources

A.1     AUSCERT advisories and alerts
            Past AUSCERT advisories and alerts can be retrieved via anonymous 
            ftp from
                ftp://ftp.auscert.org.au/pub/auscert/advisory/ 

A.2     AUSCERT's World Wide Web server
            AUSCERT maintains a World Wide Web server.  Its URL is
                http://www.auscert.org.au

A.3     AUSCERT's ftp server
            AUSCERT maintains an ftp server with an extensive range of
            tools and documents.  Please browse through it.  Its URL is
                ftp://ftp.auscert.org.au/pub/

==============================================================================
Appendix B:   Useful security tools

        There are many good tools available for checking your system.
        The list below is not a complete list, and you should NOT rely on 
        these to do ALL of your work for you.  They are intended to be only 
        a guide.  It is envisaged that you may write some site specific tools
        to supplement these.  It is also envisaged that you may look around
        on ftp servers for other useful tools.

        AUSCERT has not formally reviewed, evaluated or endorsed the tools
        described.  The decision to use the tools described is the
        responsibility of each user or organisation.

B.1     Crack
            Crack is a fast password cracking program designed to assist site 
            administrators in ensuring that users use effective passwords.
            Available via anonymous ftp from:
                ftp://ftp.auscert.org.au/pub/cert/tools/crack/*

B.2     COPS and Tiger
            These packages identify common security and configuration
            problems.  They also check for common signs of intrusion. 
            Though there is some overlap between these two packages, they
            are different enough that it may be useful to run both. Both 
            are available via anonymous ftp.
            COPS:
                ftp://ftp.auscert.org.au/pub/cert/tools/cops/1.04
            tiger:
                ftp://ftp.auscert.org.au/pub/mirrors/net.tamu.edu/tiger*

B.3     anlpasswd
            This program is a proactive password checker.  It runs a
            series of checks on passwords at the time users set them and
            refuses password that fail the tests.  It is designed to work 
            with shadow password systems.  It is available via anonymous ftp
            from:
                ftp://ftp.auscert.org.au/pub/mirror/info.mcs.anl.gov/*

B.4     tcp_wrapper
            This software gives logging and access control to most network
            services.  It is available via anonymous ftp from:
                ftp://ftp.auscert.org.au/pub/mirrors/ftp.win.tue.nl
                        /tcp_wrappers_7.2.tar.gz
        
B.5     Tripwire
            This package maintains a checksum database of important system
            files.  It can serve as an early intrusion detection system. It
            is available via anonymous ftp from:
                ftp://ftp.auscert.org.au/pub/coast/COAST/Tripwire/*

B.6     cpm 
            cpm checks to see if your network interfaces are running in 
            promiscuous mode.  If you do not normally run in this state then 
            it may be an indication that an intruder is running a network 
            sniffer on your system.  This program was designed to run on 
            SunOS 4.1.x and may also work on many BSD systems.  It is available 
            via anonymous ftp from:
               ftp://ftp.auscert.edu.au/pub/cert/tools/cpm/*

B.8     Vendor supplied security auditing packages
            Sun provides an additional security package called SUNshield. 
            Please direct enquiries about similar products to your vendor.

B.9     smrsh 
            The smrsh(8) program is intended as a replacement for /bin/sh
            in the program mailer definition of sendmail(8).  smrsh is a
            restricted shell utility that provides the ability to specify,
            through a configuration, an explicit list of executable
            programs.  When used in conjunction with sendmail, smrsh
            effectively limits sendmail's scope of program execution to
            only those programs specified in smrsh's configuration.        
            It is available via anonymous ftp from:
               ftp://ftp.auscert.org.au/pub/cert/tools/smrsh

            Note: smrsh comes bundled with Eric Allman's sendmail 8.7.1 and
            higher.

B.10    MD5
            MD5 is a message digest algorithm.  An implementation of this is 
            available via anonymous ftp from:
               ftp://ftp.auscert.org.au/pub/cert/tools/md5/*
              
B.11    rscan
            This tool checks for a number of common IRIX-specific security 
            bugs and problems. It is available via anonymous ftp from:
               ftp://ftp.auscert.org.au/pub/mirrors/ftp.vis.colostate.edu
                        /rscan/*  

B.12    SATAN
            SATAN (Security Administrator Tool for Analysing Networks) is
            a testing and reporting tool that collects information about
            networked hosts.  It can also be run to check for a number
            of vulnerabilities accessible via the network.  It is available
            via anonymous ftp from:
               ftp://ftp.auscert.org.au/pub/mirrors/ftp.win.tue.nl/satan*

B.13   logdaemon
            Written by Wietse Venema, this package includes replacements
            for rsh and rlogin daemons.  By default these versions do not
            accept wild cards in host.equiv or .rhost files.  They also
            have an option to disable user .rhost files.  logdaemon is
            available via anonymous ftp from:
               ftp://ftp.auscert.org.au/pub/mirrors/ftp.win.tue.nl/logdaemon*

B.14    portmapper/rpcbind
            These are portmapper/rpcbind replacements written by Wietse
            Venema that disallow proxy access to the mount daemon via the 
            portmapper.  Choose the one suitable for your system.  They are 
            available via anonymous ftp from:         
               ftp://ftp.auscert.org.au/pub/mirrors/ftp.win.tue.nl
                                        /portmap_3.shar.Z
               ftp://ftp.auscert.org.au/pub/mirrors/ftp.win.tue.nl
                                        /rpcbind_1.1.tar.Z

B.15    PGP Pretty Good Privacy implements encryption and authentication. 
            It is available from:
               ftp://ftp.ox.ac.uk/pub/pgp/unix/

 
B.16    chrootuid
            Allows chroot functionality.  The current version is 1.2 (at
            time of writing).  Please check for later versions.
            It is available from:
               ftp://ftp.auscert.org.au/pub/mirrors/ftp.win.tue.nl
                                        /chrooduid1.2
            A digital signature is available from:
               ftp://ftp.auscert.org.au/pub/mirrors/ftp.win.tue.nl
                                        /chrooduid1.2.asc

B.17    CGIWRAP
            It is available from:
               ftp://ftp.cc.umr.edu/pub/cgi/cgiwrap

B.18    X11R6
            It is available from:
               ftp://archie.au/X11/R6/*
               ftp://archie.au/X11/contrib/*
             or
               ftp://ftp.x.org/pub/R6/*
           
B.19    Washington University ftpd (wu-ftpd)
            This can log all events and provide users with a login banner
            and provide writable directory support in a more secure manner.  
            It is available from:
               ftp://ftp.auscert.org.au/pub/mirrors/wuarchive.wustl.edu
                        /packages/wuarchive-ftpd/*

        NOTE:  Do not install any versions prior to wu-ftp 2.4 as these are 
               extremely insecure and in some cases have been trojaned.
               Refer to the CERT advisory CA-94:07 (C.8).  

B.20    Patch 005 for BSD/386 v1.1.  
            It is available from:
               ftp://ftp.auscert.org.au/pub/mirrors/ftp.bsdi.com
                        /bsdi/patches/README
               ftp://ftp.auscert.org.au/pub/mirrors/ftp.bsdi.com
                        /bsdi/patches/?U110-005
             or
               ftp://ftp.bsdi.com/bsdi/patches/README
               ftp://ftp.bsdi.com/bsdi/patches/?U110-005
               (where ? is B or S for the Binary or Source version)

B.21    Anonymous FTP Configuration Guidelines
            The CERT document which addresses the many problems associated 
            with writable anonymous ftp directories.  It is available from:
               ftp://ftp.auscert.org.au/pub/cert/tech_tips/anonymous_ftp

==============================================================================
Appendix C:     References

C.1     Practical UNIX Security
        Simson Garfinkel and Gene Spafford
        (C) 1991 O'Reilly & Associates, Inc.

C.2     UNIX Systems Security
        Patrick Wood and Stephen Kochan
        (C) 1986 Hayden Books

C.3     UNIX system security: A Guide for Users and System Administrators
        David A. Curry
        Addison-Wesley Professional Computing Series
        May 1992.

C.4     X Window System Administrators Guide
        Chapter 4
        (C) 1992 O'Reilly & Associates, Inc.

C.5     Information Security Handbook
        William Caelli, Dennis Longley and Michael Shain
        (C) 1991 MacMillan Publishers Ltd.

C.6     Firewalls and Internet Security
        William R. Cheswick & Steven M. Bellovin
        (C) 1994 AT&T Bell Laboratories
        Addison-Wesley Publishing Company

C.7     Building Internet Firewalls
        Brent Chapman and Elizabeth Zwicky
        (C) 1995 O'Reilly & Associates, Inc.

C.8     CERT advisories are available via anonymous FTP from
           ftp://ftp.auscert.org.au/pub/cert/cert_advisories/*
        CERT vendor-initiated bulletins are available via anonymous FTP from
           ftp://ftp.auscert.org.au/pub/cert/cert_bulletins/*

C.9     UNIX System Administration Handbook (second edition)
        Evi Nemeth, Garth Snyder, Trent R. Hein and Scott Seebas
        Prentice-Hall, Englewood Cliffs (NJ), 1995

C.10    Essential System Administration
        Aeleen Frisch
        O'Reilly & Associates, Inc.

C.11    Managing Internet Information Services
        Cricket Liu, Jerry Peek, Russ Jones, Bryan Buus, Adrian Nye
        O'Reilly & Associates, Inc.

C.12    Managing NFS and NIS
        Hal Stern, O'Reilly and Associates, Inc., 1991
        
==============================================================================
Appendix D: Abbreviated Checklist

        It is intended that this short version of the checklist be used in
        conjunction with the full checklist as a progress guide (mark off the
        sections as you go so that you remember what you have done so far).

1.0   Patches
 [ ]    Installed latest patches?

2.0   Network security
 [ ]    Filtering
 [ ]    "r" commands
 [ ]    /etc/hosts.equiv
 [ ]    /etc/netgroup
 [ ]    $HOME/.rhosts
 [ ]    NFS
 [ ]    /etc/hosts.lpd
 [ ]    Secure terminals
 [ ]    Network services
 [ ]    Trivial ftp (tftp)
 [ ]    /etc/services
 [ ]    tcp_wrapper (also known as log_tcp)
 [ ]    /etc/aliases
 [ ]    Sendmail
 [ ]    majordomo
 [ ]    fingerd
 [ ]    UUCP
 [ ]    REXD
 [ ]    World Wide Web (WWW) - httpd

3.0   ftpd and anonymous ftp
 [ ]    Versions
 [ ]    Configuration
 [ ]    Anonymous ftp only
 [ ]        Configuration of your ftp server
 [ ]        Permissions
 [ ]        Writable directories
 [ ]        Disk mounting

4.0   Password and account security
 [ ]    Policy
 [ ]    Proactive Checking
 [ ]    NIS, NIS+ and /etc/passwd entries
 [ ]    Password shadowing
 [ ]    Administration
 [ ]    Special accounts
 [ ]    Root account
 [ ]    .netrc files  
 [ ]    GCOS field  

5.0   File system security
 [ ]    General
 [ ]    Startup and shutdown scripts
 [ ]    /usr/lib/expreserve
 [ ]    External file systems/devices
 [ ]    File Permissions
 [ ]    Files run by root
 [ ]    Bin ownership
 [ ]    Tiger/COPS
 [ ]    Tripwire

6.0   Vendor operating system specific security
 [ ]    SunOS 4.1.x
 [ ]        Patches
 [ ]        IP forwarding and source routing
 [ ]        Framebuffers  /dev/fb       
 [ ]        /usr/kvm/sys/*
 [ ]        /usr/kvm/crash
 [ ]        /dev/nit (Network Interface Tap)
 [ ]        Loadable drivers option
 [ ]    Solaris 2.x
 [ ]        Patches
 [ ]        IP forwarding and source routing
 [ ]        Framebuffers /dev/fbs
 [ ]    IRIX
 [ ]        Patches
 [ ]    AIX
 [ ]        Patches
 [ ]    HPUX
 [ ]        Patches
 [ ]    OSF
 [ ]        Patches
 [ ]    ULTRIX
 [ ]        Patches

7.0   Security and the X Window System
 [ ]    Problems with xdm
 [ ]    X security - General

==============================================================================
Appendix E: Shell Scripts

E.1   Script for printing the umask value for each user.

#!/bin/sh
PATH=/bin:/usr/bin:/usr/etc:/usr/ucb

HOMEDIRS=`cat /etc/passwd | awk -F":" 'length($6) > 0 {print $6}' | sort -u`
FILES=".cshrc .login .profile"

for dir in $HOMEDIRS
do
        for file in $FILES
        do
                grep -s umask /dev/null $dir/$file
        done
done

==============================================================================
Appendix F: Table of operating systems by flavour

   Operating System             SVR4-like       BSD-like         Other
   -------------------------------------------------------------------
   |                                                                 |
   | SunOS 4.1.x                                   *                 |
   |                                                                 |
   | Solaris 2.x                   *                                 |
   |                                                                 |
   | Solaris intel86 x.x           *                                 |
   |                                                                 |
   | Irix x.x                      *                                 |
   |                                                                 |
   | HP/UX x.x                     *                                 |
   |                                                                 |
   | Ultrix x.x                                    *                 |
   |                                                                 |
   | OSF x.x                       *                                 |
   |                                                                 |
   | *BSD* x.x                                     *                 |
   |                                                                 |
   | Linux x.x                     *                                 |
   |                                                                 |
   | AIX x.x                                                     *   |
   |                                                                 |
   | SCO x.x                                                     *   |
   |                                                                 |
   -------------------------------------------------------------------

==============================================================================
Appendix G: List of commands by flavour

Notes:
 1.  The commands given here are examples only.  Please consult the manual
     pages for your system if you are unsure of the consequence of any
     command.
 2.  BSD-style commands are marked as BSD commands, similarly for SVR4.
 3.  Commands which are not labelled are expected to work for both.
 4.  Full directory paths and program options may vary for different flavours
     of UNIX. If in doubt, consult your vendor documentation. 

G.1  Restart inetd

BSD commands
     # /bin/ps -aux | /bin/grep inetd | /bin/grep -v grep
     # /bin/kill -HUP <inetd-PID>

SVR4 commands
     # /bin/ps -ef | /bin/grep inetd | /bin/grep -v grep
     # /bin/kill -HUP <inetd-PID>

G.2  Ascertain which services are registered with the portmapper

     # /usr/bin/rpcinfo -p  

G.3  Rebuild alias maps

     # /usr/bin/newaliases

   If you run NIS (YP), you will then need to rebuild your maps to have the
   change take effect over all clients:
     # (cd /var/yp; /usr/bin/make aliases)

G.4  Test whether sendmail wizard password is enabled

     % telnet hostname 25
     wiz
     debug
     kill
     quit
     %

   You should see the response "5nn error return"  (e.g., "500 Command
   unrecognized") after each of the commands  'wiz', 'debug' and 'kill'. 
   Otherwise, your version of sendmail may be vulnerable. If you are unsure
   whether your version is vulnerable, update it.

G.5  Set sendmail log level to 9

   Include lines describing the log level (similar to the following two) in
   the options part of the general configuration information section of the
   sendmail configuration file:
     # log level
     OL9   

   The log level syntax changed in sendmail 8.7 to:
     # log level
     O LogLevel=9

G.6  Set syslog log level for mail messages

   Include lines describing the logging required (similar to the following
   two) in the syslog.conf file: 
     mail.info                       /dev/console
     mail.info                       /var/adm/messages 

   For the change to take effect, you must then instruct syslog to reread
   the configuration file.  

BSD commands
   Get the current PID of syslog:
     # /bin/ps -aux | /bin/grep syslogd | /bin/grep -v grep
   Then tell syslog to reread its configuration file:
     # /bin/kill -HUP <syslog-PID>

SVR4 commands:
   Get the current PID of syslog:
     # /bin/ps -ef | /bin/grep syslogd | /bin/grep -v grep
   Then tell syslog to reread its configuration file:
     # /bin/kill -HUP <syslog-PID>

   NOTE: In the logs, look for error messages like:
         - mail to or from a single pipe ("|")
         - mail to or from an obviously invalid user (e.g., bounce or blah)

G.7  (Rebuilding and) restarting sendmail(8)

   To rebuild the frozen configuration file, firstly do:
     # /usr/lib/sendmail -bz

   NOTE: The above process does not apply to sendmail v8.x which does not
         support frozen configuration files.

   To restart sendmail(8), you should kill *all* existing sendmail(8) 
   processes by sending them a TERM signal using kill, then restart
   sendmail(8).  

BSD commands
   Get the pid of every running sendmail process:
     # /bin/ps -aux | /bin/grep sendmail | /bin/grep -v grep
   Kill every running sendmail process and restart sendmail:
     # /bin/kill <pid>     #pid of every running sendmail process
     # /usr/lib/sendmail -bd -q1h

SVR4 commands
   Get the pid of every running sendmail process:
     # /bin/ps -ef | /bin/grep sendmail | /bin/grep -v grep
   Kill every running sendmail process and restart sendmail:
     # /bin/kill <pid>     #pid of every running sendmail process
     # /usr/lib/sendmail -bd -q1h

G.8  Test whether ftpd supports SITE EXEC 

   For normal users:

     % telnet localhost 21
     USER username
     PASS password
     SITE EXEC

   For anonymous users:

     % telnet localhost 21
     USER ftp
     PASS username@domainname.au
     SITE EXEC

   You should see the response "5nn error return"  (e.g., "500 'SITE
   EXEC' command not understood").  If your ftp daemon has SITE EXEC
   enabled, make sure you have the most recent version of the daemon (e.g.,
   wu-ftp 2.4).  Older versions of ftpd allow any user to gain shell access
   using the SITE EXEC command.  Use QUIT to end the telnet session.

G.9  Ascertain whether anonymous ftp is enabled

     % ftp localhost
     Connected to localhost
     220 hostname FTP server ready
     Name (localhost:username):  anonymous
     331 Guest login ok, send username as password
     Password:  user@domain.au 
     230 Guest login ok, access restrictions apply.
     Remote system type is UNIX.
     Using binary mode to transfer files.
     ftp>

G.10  Ensure that * in the password field is correctly implemented 
   
   1. Try using NIS with the '*' in the password field for example:
        +:*:0:0:::      
      If NIS users cannot log in to that machine, remove the '*' and  try
      the next test.

   2. With the '*' removed, try logging in again.  If NIS users can log in
      AND you can also log in unauthenticated as the user '+', then your
      implementation is vulnerable.  Contact the vendor for more information. 
      If NIS users can log in AND you cannot log in as the user '+', your
      implementation should not be vulnerable to this problem.

G.11  Find .exrc files
                   
     # /bin/find /  -name '.exrc' -exec /bin/cat {} \; -print

   See also G.19.

G.12  Locate and print .forward files

     # /bin/find / -name '.forward' -exec /bin/cat {} \; -print

   See also G.19.

G.13  Remove execute permission on /usr/lib/expreserve

     # /bin/chmod 400 /usr/lib/expreserve

G.14  Set ownership and permissions for /tmp correctly

     # /bin/chown root /tmp
     # /bin/chgrp 0 /tmp
     # /bin/chmod 1777 /tmp

   NOTE: This will NOT recursively set the sticky bit on sub-directories
         below /tmp, such as /tmp/.X11-unix and /tmp/.NeWS-unix; you may 
         have to set these manually or through the system startup files.

G.15  Find group and world writable files and directories

     # /bin/find / -type f \( -perm -2 -o -perm -20 \) -exec ls -lg {} \;

     # /bin/find / -type d \( -perm -2 -o -perm -20 \) -exec ls -ldg {} \;

   See also G.19.

G.16  Find files with the SUID or SGID bit enabled

     # /bin/find / -type f \( -perm -004000 -o -perm -002000 \) \
       -exec ls -lg {} \;

   See also G.19.

G.17  Find normal files in /dev

     # /bin/find /dev -type f -exec ls -l {} \;

   See also G.19.

G.18  Find block or character special files

     # /bin/find / \( -type b -o -type c \) -print | grep -v '^/dev/'

   See also G.19.

G.19  Avoid NFS mounted file systems when using /bin/find

     # /bin/find / \( \! -fstype nfs -o -prune \) <expression>

  As an example, <expression> could be
     -type f \( -perm -004000 -o -perm -002000 \) -exec ls -lg {} \;


==============================================================================
The AUSCERT team have made every effort to ensure that the information 
contained in this checklist is accurate.  However, the decision to use the 
tools and techniques described is the responsibility of each user or 
organisation.  The appropriateness of each item for an organisation or 
individual system should be considered before application in conjunction with 
local policies and procedures.  AUSCERT takes no responsibility for the 
consequences of applying the contents of this document.  

AUSCERT acknowledges technical input and review of this document by CERT
Coordination Center and DFN-CERT and comments from users of this document.

Permission is granted to copy and distribute this document provided that The 
University of Queensland copyright is acknowledged.

(C) Copyright 1995 The University of Queensland
==============================================================================

If you believe that your system has been compromised, contact AUSCERT or your
representative in FIRST (Forum of Incident Response and Security Teams).

Internet Email: auscert@auscert.org.au
AUSCERT Hotline:     (07) 3365 4417    (International: + 61 7 3365 4417)
      Facsimile:     (07) 3365 4477
          AUSCERT personnel answer during business hours (AEST - GMT+10:00),
          on call after hours for emergencies.
                  

Australian Computer Emergency Response Team
c/- Prentice Centre
The University of Queensland
Brisbane, Queensland 4072.
Australia

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