I wanted to do a quick post on an important security bulletin.  It’s Microsoft Security Bulletin MS09-018 – Critical.  This security update is to address a vulnerability in Active Directory.  I’m pasting the Executive Summary below, but I highly recommend that you read the entire bulletin and apply the updates.

Executive Summary

This security update resolves two privately reported vulnerabilities in implementations of Active Directory on Microsoft Windows 2000 Server and Windows Server 2003, and Active Directory Application Mode (ADAM) when installed on Windows XP Professional and Windows Server 2003. The more severe vulnerability could allow remote code execution. An attacker who successfully exploited this vulnerability could take complete control of an affected system remotely. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Firewall best practices and standard default firewall configurations can help protect networks from attacks that originate outside the enterprise perimeter. Best practices recommend that systems that are connected to the Internet have a minimal number of ports exposed.

This security update is rated Critical for all supported editions of Microsoft Windows 2000 Server, and rated Important for supported versions of Windows XP Professional and Windows Server 2003. For more information, see the subsection, Affected and Non-Affected Software, in this section.

The security update addresses the vulnerability by correcting the way that the LDAP service allocates and frees memory while processing specially crafted LDAP or LDAPS requests.

Recommendation. The majority of customers have automatic updating enabled and will not need to take any action because this security update will be downloaded and installed automatically. Customers who have not enabled automatic updating need to check for updates and install this update manually. For information about specific configuration options in automatic updating, see Microsoft Knowledge Base Article 294871.

For administrators and enterprise installations, or end users who want to install this security update manually, Microsoft recommends that customers apply the update immediately using update management software, or by checking for updates using the Microsoft Update service.

Please apply this update to your Windows 2000 and Server 2003 domain controllers at your earliest opportunity.