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

From Oracle Linux 5 Security Technical Implementation Guide

Associated with: CCI-000366

SV-63671r2_rule All shells referenced in /etc/passwd must be listed in the /etc/shells file, except any shells specified for the purpose of preventing logins.

Vulnerability 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: Determine which shells are permitted for use by users: # more /etc/shells Note: /usr/bin/false, /bin/false, /dev/null, /sbin/nologin, /bin/sync, /sbin/halt, /sbin/shutdown, (and equivalents) cannot be placed in the /etc/shells file. Determine which shells are being used: # more /etc/passwd (optionally shells found in /etc/passwd can be grepped for in /etc/shells) If any shells are found that are not in /etc/shells, or if false shells are found in /etc/shells, then this is a finding.

Fix text

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. Example: # chsh -s /bin/bash testuser

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