5.3.2 Lockout for failed password attempts - 'auth required pam_tally2.so onerr=fail audit silent deny=5 unlock_time=900'

Information

Lock out users after n unsuccessful consecutive login attempts. The first sets of changes are
made to the PAM configuration files. The second set of changes are applied to the program
specific PAM configuration file. The second set of changes must be applied to each program
that will lock out users. Check the documentation for each secondary program for
instructions on how to configure them to work with PAM.

Set the lockout number to the policy in effect at your site.

Rationale:

Locking out user IDs after n unsuccessful consecutive login attempts mitigates brute force
password attacks against your systems.

Solution

Set password lockouts to conform to site policy. Many distributions provide tools for
updating PAM configuration, consult your documentation for details. If no tooling is
provided edit the appropriate /etc/pam.d/ configuration file and add or modify the
pam_tally2.so or pam_faillock.so lines as appropriate:

auth required pam_tally2.so onerr=fail audit silent deny=5 unlock_time=900

auth required pam_faillock.so preauth audit silent deny=5 unlock_time=900
auth sufficient pam_unix.so
auth [default=die] pam_faillock.so authfail audit deny=5 unlock_time=900
auth sufficient pam_faillock.so authsucc audit deny=5 unlock_time=900

Notes:

Consult your documentation for the appropriate PAM file and module.

Additional module options may be set, recommendation only covers those listed here.

If a user has been locked out because they have reached the maximum consecutive failure
count defined by deny= in the pam_tally2.so or pam_faillock.so module, the user can be
unlocked by issuing the command pam_tally2 -u <username> --reset or faillock -u -
-reset respectively. This command sets the failed count to 0, effectively unlocking the user.

Use of the "audit" keyword may log credentials in the case of user error during
authentication. This risk should be evaluated in the context of the site policies of your
organization.

See Also

https://workbench.cisecurity.org/files/2420