Vulnerability Discussion

Without configuring a local cache of revocation data, there is the potential to allow access to users who are no longer authorized (users with revoked certificates).

Check

Verify Ubuntu 22.04 LTS, for PKI-based authentication, uses local revocation data when unable to access it from the network by using the following command:

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

$ grep cert_policy /etc/pam_pkcs11/pam_pkcs11.conf | grep -E -- 'crl_auto|crl_offline'
cert_policy = ca,signature,ocsp_on,crl_auto;

If "cert_policy" is not set to include "crl_auto" or "crl_offline", is commented out, or is missing, this is a finding.

Fix

Configure Ubuntu 22.04 LTS, for PKI-based authentication, to use local revocation data when unable to access the network to obtain it remotely.

Add or update the "cert_policy" option in "/etc/pam_pkcs11/pam_pkcs11.conf" to include "crl_auto" or "crl_offline".

cert_policy = ca,signature,ocsp_on, crl_auto;

If the system is missing an "/etc/pam_pkcs11/" directory and an "/etc/pam_pkcs11/pam_pkcs11.conf", find an example to copy into place and modify accordingly at "/usr/share/doc/libpam-pkcs11/examples/pam_pkcs11.conf.example.gz".