Web security protocols open to MITM attacks

Researchers have discovered a weakness in some of the protocols used to secure web traffic and e-commerce data over the Internet, arising from a flaw in their specification.

The vulnerabilities in the Transport Layer Security (TLS) and the Datagram TLS variant were discoveredby researchers Nadhem AlFardan and Kenny Paterson at the Information Security Group at Royal Holloway, University of London. (pdf) 

All TLS and DTLS ciphersuites that include cipher block chaining mode encryption are potentially vulnerable to the attacks, the researchers said.

A full plain text recovery is possible with OpenSSL, according to the researchers, and a partial one with GnuTLS.

However, the researchers noted that "the attacks can only be carried out by a determined attacker who is located close to the machine" to be compromised.

As such, "the attacks do not pose a signficant danger to ordinary users of TLS in their current form".

However, the researchers expected the attack to improve with time, or morph into an entirely new form of compromise.

The researchers named the attacks "Lucky Thirteen" after the thirteen bytes of header information in the TLS MAC calculation that makes the compromise possible.

"This is what passes for humour amongst cryptographers," the researchers said.

A fix for the flaw and two other security issues has been released by OpenSSL. Other organisations such as NSS, GnuTLS, CyaSSL, Opera and BouncyCastle have also issued patches.