Symptom
SSL sessions with mutual authentication required, meaning both server and client need to present a certificate to authenticate, will fail to get decrypted and will possibly get blocked.
Conditions
SSL Decrpytion Policy enabled and configured to decrypt traffic (either Decrypt-Resign or Decrpyt with Known Key) and traffic passing through FTD requiring Client Authentication.
Further Problem Description
Client certificates are not supported by the Firepower System, which will make any SSL traffic fail to be decrypted and will possibly get blocked whenever the Client Certificate is part of the session establishment.
