In socat before 2.0.0-b9, in the OpenSSL address implementation, the hard coded 1024 bit DH p parameter was not prime. It may be possible for an eavesdropper to recover the shared secret from a key exchange (CVE-2016-2217).
In socat before 2.0.0-b9, a stack overflow vulnerability was found that can be triggered when command line arguments are longer than 512 bytes. This vulnerability can only be exploited when an attacker is able to inject data into socat's command line.