Vulnerability Note VU#592796

Mozilla Network Security Services (NSS) fails to properly handle the client master key

Original Release date: 07 Mar 2007 | Last revised: 05 Apr 2007


A vulnerability in the way Mozilla Network Security Services (NSS) handles the client master key may lead to execution of arbitrary code.


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, Firefox, 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.

Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
Fedora ProjectAffected-07 Mar 2007
Gentoo LinuxAffected-05 Apr 2007
Mandriva, Inc.Affected-07 Mar 2007
MozillaAffected-27 Feb 2007
Red Hat, Inc.Affected-07 Mar 2007
rPathAffected-07 Mar 2007
Slackware Linux Inc.Affected-05 Apr 2007
Sun Microsystems, Inc.Affected-05 Apr 2007
SUSE LinuxAffected-07 Mar 2007
UbuntuAffected-07 Mar 2007
If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A N/A



This vulnerability was reported in Mozilla Foundation Security Advisory 2007-06. Mozilla credits iDefense with reporting this issue.

This document was written by Chris Taschner.

Other Information

  • CVE IDs: CVE-2007-0009
  • Date Public: 23 Feb 2007
  • Date First Published: 07 Mar 2007
  • Date Last Updated: 05 Apr 2007
  • Severity Metric: 12.72
  • Document Revision: 57


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