Title

The /etc/shells file must exist on AIX systems. (Cat II impact)

Discussion

The shells file (or equivalent) lists approved default shells. It helps provide layered defense to the security approach by ensuring users cannot change their default shell to an unauthorized unsecure shell.

Check Content

AIX ships the following shells that should be considered as "approved" shells: /bin/sh /bin/bsh /bin/csh /bin/ksh /bin/tsh /bin/ksh93 /usr/bin/sh /usr/bin/bsh /usr/bin/csh /usr/bin/ksh /usr/bin/tsh /usr/bin/ksh93 /usr/bin/rksh /usr/bin/rksh93 /usr/sbin/uucp/uucico /usr/sbin/sliplogin /usr/sbin/snappd ISSO/SA may install other shells. Ask ISSO/SA for other approved shells other than the shells shipped by AIX. Check if file "/etc/shells" exists by running: # ls -la /etc/shells rw-r--r-- 1 bin bin 111 Jun 01 2015 /etc/shells If "/etc/shells" file does not exist, this is a finding. Verify that "/etc/shells" only contains approved shells: # cat /etc/shells /bin/csh /bin/ksh /bin/psh /bin/tsh /bin/bsh /usr/bin/csh /usr/bin/ksh /usr/bin/tsh /usr/bin/bsh If "/etc/shells" file contains a non-approved shell, this is a finding. Check "/etc/security/login.cfg" for the shells attribute value of "usw:" stanza: # lssec -f /etc/security/login.cfg -s usw -a shells usw shells=/bin/sh,/bin/bsh,/bin/csh,/bin/ksh,/bin/tsh,/bin/ksh93,/usr/bin/sh,/usr/bin/bsh,/usr/bin/csh,/usr/bin/ksh,/usr/bin/tsh,/usr/bin/ksh93,/usr/bin/rksh,/usr/bin/rksh93,/usr/sbin/uucp/uucico,/usr/sbin/sliplogin,/usr/sbin/snappd If the shells attribute value does not exist or is empty, this is a finding. If the returned shells attribute value contains a shell that is not defined in "/etc/shells" file, this is a finding. If the returned shells attribute value contains a non-approved shell, this is a finding.

Fix Text

Run the following command to set shells attribute for stanza usw in "/etc/security/login.cfg": # chsec -f /etc/security/login.cfg -s usw -a shells=<list of approved shells separated by comma> Create the "/etc/shells" file and add all approved shells there, one shell per line: # vi /etc/shells Change the ownership and mode-bit of "/etc/shells": # chown bin.bin /etc/shells # chmod 644 /etc/shells

Additional Identifiers

Rule ID: SV-215408r991589_rule

Vulnerability ID: V-215408

Group Title: SRG-OS-000480-GPOS-00227

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.