PAM-PKCS#11 vulnerable to authentication bypass with default value for `cert_policy` (`none`)

Vulnerability Description

PAM-PKCS#11 is a Linux-PAM login module that allows a X.509 certificate based user login. Prior to version 0.6.13, if cert_policy is set to none (the default value), then pam_pkcs11 will only check if the user is capable of logging into the token. An attacker may create a different token with the user's public data (e.g. the user's certificate) and a PIN known to the attacker. If no signature with the private key is required, then the attacker may now login as user with that created token. The default to *not* check the private key's signature has been changed with commit commi6638576892b59a99389043c90a1e7dd4d783b921, so that all versions starting with pam_pkcs11-0.6.0 should be affected. As a workaround, in `pam_pkcs11.conf`, set at least `cert_policy = signature;`.

References

• https://github.com/OpenSC/pam_pkcs11/security/advisories/GHSA-8r8p-7mgp-vf56
• https://github.com/OpenSC/pam_pkcs11/commit/470263258d1ac59c5eade439c4d9caba0097e6e6
• https://github.com/OpenSC/pam_pkcs11/commit/b665b287ff955bbbd9539252ff9f9e2754c3fb48
• https://github.com/OpenSC/pam_pkcs11/commit/d9530167966a77115db6e885d459382a2e52ee9e
• https://github.com/OpenSC/pam_pkcs11/releases/tag/pam_pkcs11-0.6.13