Vulnerability Discussion

By limiting the number of failed access attempts, the risk of unauthorized system access via user password guessing, otherwise known as brute-force attacks, is reduced. Limits are imposed by locking the account.

The pam_tally2.so module maintains a count of attempted accesses. This includes user name entry into a logon field as well as password entry. With counting access attempts, it is possible to lock an account without presenting a password into the password field. This should be taken into consideration as it poses as an avenue for denial of service.

Check

Verify the SUSE operating system locks a user account after three consecutive failed access attempts until the locked account is released by an administrator.

Check that the system locks a user account after three consecutive failed login attempts using the following command:

# grep pam_tally2.so /etc/pam.d/common-auth
auth required pam_tally2.so onerr=fail deny=3

If no line is returned or the line is commented out, this is a finding.

If the line is missing "onerr=fail", this is a finding.

If the line has "deny" set to a value other than 1, 2, or 3, this is a finding.

Check that the system resets the failed login attempts counter after a successful login using the following command:

# grep pam_tally2.so /etc/pam.d/common-account
account required pam_tally2.so

If the account option is missing, or commented out, this is a finding.

Fix

Configure the operating system to lock an account when three unsuccessful access attempts occur.

Modify the first line of the auth section "/etc/pam.d/common-auth" file to match the following lines:

auth required pam_tally2.so onerr=fail silent audit deny=3

Add or modify the following line in the /etc/pam.d/common-account file:
account required pam_tally2.so

Note: Manual changes to the listed files may be overwritten by the "pam-config" program. The "pam-config" program should not be used to update the configurations listed in this requirement.