You Might Not Know You Are Still Using SSLv2.0

July 1, 2016

Netscape Communications invented Secure Sockets Layer (SSL) protocol in 1994. It has been de facto standard for cryptographic protocol since then. Over the years the protocol has evolved (SSLv2.0 -> SSLv3.0 -> TLSv1.0 -> TLSv1.1 -> TLSv1.2) to increase security.

Today, SSLv2.0 no longer provides a sufficiently high level of security. SSLv2.0 deficiencies include the following:

  • Message authentication uses MD5. Most security-aware users have already moved away from any use of MD5.
  • Handshake messages are not protected. This permits a man-in-the-middle to trick the client into picking a weaker cipher suite than it would normally choose.
  • Message integrity and message encryption use the same key, which is a problem if the client and server negotiate a weak encryption algorithm.
  • Sessions can be easily terminated. A man-in-the-middle can easily insert a TCP FIN to close the session, and the peer is unable to determine whether or not it was a legitimate end of the session.

It's been over 20 years since SSLv2.0 was published, and it's been over 5 years since RFC 6176 deprecated SSLv2.0. However many people are still using the protocol, even though they might not be aware of it.

In June 2016, less than 2% of firewalls reported receiving SSLv2.0 Server Hello message:

In June 2016, more than 40% of firewalls reported receiving SSLv2.0 Client Hello message:

SSLv2.0 is insecure and can damage the system. Dell SonicWALL urges all our customers to review their (client/server) software settings and stop using SSLv2.0 immediately.