Microsoft Security Bulletin MS07-040 - Critical
This update resolves three privately reported vulnerabilities. Two of these vulnerabilities could allow remote code execution on client systems with .NET Framework installed, and one could allow information disclosure on Web servers running ASP.NET. In all remote code execution cases, users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.
This security update addresses two vulnerabilities by modifying the way .NET Framework addresses buffer allocation. For more information about the vulnerabilities, see the Frequently Asked Questions (FAQ) subsection for the specific vulnerability entry under the next section, Vulnerability Information.
Recommendation: Microsoft recommends that customers apply the update immediately.
http://www.microsoft.com/technet/security/bulletin/ms07-040.mspx