Upgrading to 12.8.08.01 causes a user to be able to login and use another user's valid certificate to authenticate.
In order for this issue to occur, the user's login and the certificate must be valid.
When the auth scheme is configured to use custom certificate mapping, matching the forms user and the certificate user does not take place and the user is authenticated when authentication should fail.
This is a known issue and will be resolved in a future release.