Software Engineering Institute

The SSLv2 protocol uses a client master key to generate all subsequent session keys. The client master key is created using a public key recieved from the server during phase one of the SSL handshake. Mozilla NSS library contains a vulnerability in the way malformed SSLv2 server messages related to the public key are handled that may result in a buffer overflow. According to the Mozilla Foundation Security Advisory 2007-06:

SSL clients such as Firefox and Thunderbird can suffer a buffer overflow if a malicious server presents a certificate with a public key that is too small to encrypt the entire "Master Secret". Exploiting this overflow appears to be unreliable but possible if the SSLv2 protocol is enabled.

Note that this vulnerability may affect any application that uses the Mozilla NSS library.

A remote, unauthenticated attacker may be able to execute arbitrary code with the privileges of the user who is running the vulnerable application or cause a denial of service.

Apply an update
According to the Mozilla Foundation Security Advisory 2007-06, this vulnerability is addressed in Firefox 2.0.0.2, Firefox 1.5.0.10, SeaMonkey 1.0.8, and NSS 3.11.5.

Disable SSLv2

Disabling support for the SSLv2 protocol appears to prevent exploitation of this vulnerability. Instructions for disabling the SSLv2 protocol support in Firefox and Thunderbird can be found in the Mozilla Foundation Security Advisory 2007-06.