CVE-2018-1113

Setup in Fedora and Red Hat Enterprise Linux added /sbin/nologin and /usr/sbin/nologin to /etc/shells. This violates security assumptions made by pam_shells and some daemons which allow access based on a user's shell being listed in /etc/shells. Under some circumstances, users which had their shell changed to /sbin/nologin could still access the system.

Preventing a user from accessing the system without deleting their account is not a simple matter. For utmost security, the account should be deleted. Short of this, we recommend a three-pronged approach:

• change the user's login shell to a harmless command that is not in "/etc/shells" (for example "/bin/false") to prevent commands being run on their behalf
• lock the user's password with "usermod -L" to prevent authentication with pam services
• prevent access to the user's home directory with "chmod 0" or "chown root" and "chmod 700" to prevent authentication with ssh keys etc

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.