>> In HAProxy, this flag is currently statically disabled by default in >> src/ssl_sock.c line 2539. Thus, when used with older OpenSSL versions >> than 1.0.1r or 1.0.2f, users could be vulnerable. > > I don't see it. Can you please elaborate what exact commit ID your are > refering to?
You are probably refering to the github fork, which is as always outdated, and where line 2539 points to the local definition of SSL_OP_SINGLE_DH_USE: #ifndef SSL_OP_SINGLE_ECDH_USE #define SSL_OP_SINGLE_ECDH_USE 0 #endif You are misunderstanding this code. We define SSL_OP_SINGLE_ECDH_USE when the openssl headers don't define it (which is when the openssl release doesn't support SSL_OP_SINGLE_ECDH_USE - older than 1.0.0), to avoid #ifdef hell in the ssl_sock_prepare_ctx function. So when OpenSSL supports SSL_OP_SINGLE_ECDH_USE, we *do* set it. Lukas