The OpenSSL address implementation in Socat 1.7.3.0 and 2.0.0-b8 does not use a prime number for the DH, which makes it easier for remote attackers to obtain the shared secret.
https://security.gentoo.org/glsa/201612-23
http://www.openwall.com/lists/oss-security/2016/02/04/1
http://www.openwall.com/lists/oss-security/2016/02/01/4
http://www.dest-unreach.org/socat/contrib/socat-secadv7.html