Mozilla Patches RSA Crypto Flaw

Mozilla released an update to its Firefox browser, Thunderbird, SeaMonkey, and Network Security Service (NSS) software today that patches vulnerabilities in its implementation of RSA and X.509 cryptography that make Mozilla clients susceptible to man-in-the-middle attacks.

"This is a very real, very serious attack," says Thomas Ptacek, a researcher with Matasano Security. "I can create a certificate for any Website that says anything I want. I can fix the certificate so any of the millions of Firefox browsers deployed out there will believe it. Then I can sell that certificate to a phisher."

Security researchers have been debating the possible impact of the flaw since Bell Labs first reported it. (See Crypto Flaw Prone to Spoofing.) Window Snyder, head of Mozilla's security operations, last week said Mozilla was revisiting its own code to see if it was vulnerable. Since then, several products have been found to have the vulnerability, including AppGate Network Security's AppGate version 7.1.5; F5 Networks' BIG-IP 4.x and 9.x and WANjet; OpenWall's GNU/Linux; OpenSSL; and Fedora Core 5 Linux.

And this is only the tip of the iceberg, security researchers say. Expect more vendors to come out with advisories on their RSA implementations in coming days. It's no surprise that Mozilla would be out in front on a patch: Mozilla prides itself in turning around patches quickly.

"Everyone is almost certainly scrambling to audit their implementations," says Dan Kaminsky, an independent researcher. "This is an obscure fault, but yeah, it's a pretty nasty one."

Ptacek argues this vulnerability has been "well-understood" since the mid-1980's. "The problem is that cryptographic code is incredibly hard to write correctly and incredibly hard to verify." He also notes there are multiple variants on this type of attack.

The flaw takes advantage of implementation errors in RSA signature verification, which basically let an attacker forge a digital signature and pretend to be a legitimate Website with fake digital certificates.

Mozilla's update includes Firefox 1.5.0.7, Thunderbird 1.5.0.7, SeaMonkey 1.0.5, and Network Security Service (NSS) 3.11.3.

Meanwhile, a new Web security tool promises to stop this type of attack. GreenBorder Pro, a new software package from GreenBorder Technologies, will be released on Monday for Firefox, according to a GreenBorder spokesperson. "It will prevent any man-in-the-middle attackers who exploit this vulnerability to push code onto a PC -- by masquerading as somebody else -- from being able to permanently install or steal data," says the spokesperson.

— Kelly Jackson Higgins, Senior Editor, Dark Reading