Cis Ubuntu1604 V200 5 4 2

Ensure lockout for failed password attempts is configured

Profile Applicability:

• Level 1 - Server
• Level 1 - Workstation

Assessment Status: Automated

Description

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.

• deny=n - n represents the number of failed attempts before the account is locked
• unlock_time=n - n represents the number of seconds before the account is unlocked
• audit - Will log the user name into the system log if the user is not found.
• silent - Don't print informative messages. Set the lockout number and unlock time in accordance with local site policy.

Rationale

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

Audit Procedure

Command Line

Verify password lockouts are configured. These settings are commonly configured with the pam_tally2.so modules found in /etc/pam.d/common-auth:

grep "pam_tally2" /etc/pam.d/common-auth

Expected output:

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

Verify the pam_deny.so module and pam_tally2.so modules are included in /etc/pam.d/common-account:

grep -E "pam_(tally2|deny)\.so" /etc/pam.d/common-account

Expected output:

account requisite                       pam_deny.so
account required                        pam_tally2.so

Remediation

Command Line

Edit the /etc/pam.d/common-auth file and add the auth line below:

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

Edit the /etc/pam.d/common-account file and add the account lines below:

account    requisite    pam_deny.so
account    required     pam_tally2.so

Additional Information

• Add pam_tally2 to the account section account required pam_tally2.so for the counter to reset to 0 when using sudo.
• 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.
• If a user has been locked out because they have reached the maximum consecutive failure count defined by deny= in the pam_tally2.so module, the user can be unlocked by issuing the command /sbin/pam_tally2 -u <username> --reset. This command sets the failed count to 0, effectively unlocking the user.

References

None

CIS Controls

Profile

• Level 1 - Server
• Level 1 - Workstation