Alexander E. Patrakov discovered an issue in strongSwan, an IKE/IPsec suite used to establish IPsec protected links. When an IKEv2 client authenticates the server with certificates and the client authenticates itself to the server using pre-shared key or EAP, the constraints on the server certificate are only enforced by the client after all authentication steps are completed successfully. A rogue server which can authenticate using a valid certificate issued by any CA trusted by the client could trick the user into continuing the authentication, revealing the username and password digest or even the cleartext password .