While investigating bug PROTON-2014, we discovered that under some circumstances Apache Qpid Proton versions 0.9 to 0.27.0 (C library and its language bindings) can connect to a peer anonymously using TLS *even when configured to verify the peer certificate* while used with OpenSSL versions before 1.1.0. This means that an undetected man in the middle attack could be constructed if an attacker can arrange to intercept TLS traffic.