PJSIP is a free and open source multimedia communication library written in C. Prior to version 2.17, on GnuTLS builds, the SIP TLS transport (sip_transport_tls) can accept connections with invalid or untrusted certificates even when the application explicitly enables certificate verification via verify_server = PJ_TRUE or verify_client = PJ_TRUE. This issue has been patched in version 2.17.