Ubuntu 20.04 LTS must be configured such that Pluggable Authentication Module (PAM) prohibits the use of cached authentications after one day.

If cached authentication information is out of date, the validity of the authentication information may be questionable.

Note: If smart card authentication is not being used on the system, this is not applicable.

Verify that PAM prohibits the use of cached authentications after one day with the following command:

$ sudo grep offline_credentials_expiration /etc/sssd/sssd.conf /etc/sssd/conf.d/*.conf offline_credentials_expiration = 1

If "offline_credentials_expiration" is not set to a value of "1" in "/etc/sssd/sssd.conf" or in a file with a name ending in .conf in the "/etc/sssd/conf.d/" directory, this is a finding.

Configure PAM to prohibit the use of cached authentications after one day. Add or change the following line in "/etc/sssd/sssd.conf" just below the line "[pam]":

offline_credentials_expiration = 1

Note: It is valid for this configuration to be in a file with a name that ends with ".conf" and does not begin with a "." in the "/etc/sssd/conf.d/" directory instead of the "/etc/sssd/sssd.conf" file.