Title

All shells referenced in /etc/passwd must be listed in the /etc/shells file, except any shells specified for the purpose of preventing logins. (Cat II impact)

Discussion

The shells file 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

Confirm the login shells referenced in the /etc/passwd file are listed in the /etc/shells file. Procedure: # for USHELL in `cut -d: -f7 /etc/passwd`; do if [ $(grep -c "${USHELL}" /etc/shells) == 0 ]; then echo "${USHELL} not in /etc/shells"; fi; done The /usr/bin/false, /bin/false, /dev/null, /sbin/nologin, /bin/sync, /sbin/halt, /sbin/shutdown, (and equivalents), and sdshell will be considered valid shells for use in the /etc/passwd file, but will not be listed in the /etc/shells file. If a shell referenced in /etc/passwd is not listed in the shells file, excluding the above mentioned shells, this is a finding.

Fix Text

Use the YaST > Security and Users > User and Group Management module to change the default shell of any account in error to an acceptable shell. OR Use the "chsh" utility or edit the /etc/passwd file and correct the error by changing the default shell of the account in error to an acceptable shell name contained in the /etc/shells file.

Additional Identifiers

Rule ID: SV-45171r1_rule

Vulnerability ID: V-917

Group Title: GEN002140

Expert Comments

CCIs tied to check.

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