Software Engineering Institute

The SSLv2 protocol uses a client master key to generate all subsequent session keys. The validity of the client master key is determined during phase one of the SSL handshake. Mozilla NSS library contains a vulnerability in the way client master keys with invalid length values are handled that may result in a buffer overflow. According to the Mozilla Foundation Security Advisory (MFSA) 2007-06:

Servers that use NSS for the SSLv2 protocol can be exploited by a client that presents a "Client Master Key" with invalid length values in any of several fields that are used without adequate error checking. This can lead to a buffer overflow that presumably could be exploitable.

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. SSLv2 is disabled by default in Firefox 2.