IETF Finds Fix For SSL Security Vulnerability

The Internet Engineering Task Force (IETF) has finished work on a fix to a vulnerability in the Secure Sockets Layer (SSL) protocol security researchers uncovered last August.

The vulnerability partially invalidates the SSL lock and allows attacks that could compromise sites that use SSL for security – including banking sites, and back-office systems that use web services-based protocols. The issue was uncovered by Steve Dispensa and Marsh Ray, who work for two-factor authentication provider PhoneFactor.

“The bug allows a man-in-the-middle to insert some malicious data at the beginning of a vulnerable SSL / TLS connection, but does not allow him to directly read the data sent by the legitimate parties,” explained Ray. “This capability is referred to as a “blind plaintext injection attack”. Initially, it was hoped that this limited capability would offer some mitigation. Unfortunately, it seems that HTTPS is particularly strongly affected because of its design and an effective attack on the Twitter HTTPS API was demonstrated shortly after the vulnerability was publicly disclosed.”

A copy of the IETF draft can be found here. After incorporating feedback from the TLS community, the proposed fix was approved by the Internet Engineering Steering Group (IESG) on January 7, 2010. The IESG is responsible for the technical management of IETF activities and the Internet standards process. The decision means customers can now begin to deliver patches that implement IETF’s change.

“Because of the large number and variety of systems affected, substantial interoperability testing (for the SSL extension) will be conducted by many vendors before they feel comfortable releasing a patch,” Ray said. “Some interoperability testing has already been done with preliminary versions of the patch, but another round of testing is occurring now that the details of the fix have been finalised by the IETF.”

“Some of the open source TLS implementations (OpenSSL, GnuTLS) have fixes in their publicly-visible repositories, but have not released a formal patch as of right now,” he added. “Most of the larger vendors (open source and otherwise) have been given several months’ head start on implementing the fix, so they should not be starting from zero at this point.”

The company has developed a page to track the deployment of patches for the issue. PhoneFactor’s paper on the vulnerability can be viewed here (PDF).