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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-917	GEN002140	SV-63671r2_rule		Medium

Description
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.

STIG	Date
Oracle Linux 5 Security Technical Implementation Guide	2017-03-01

Details

Check Text ( C-52291r2_chk )
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.

Check Text ( C-52291r2_chk )

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 (F-54251r1_fix)
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