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             AUSCERT External Security Bulletin Redistribution

      Vulnerability in Active Directory Could Allow Denial of Service
                              9 February 2011


        AusCERT Security Bulletin Summary

Product:           Active Directory
Publisher:         Microsoft
Operating System:  Windows Server 2003
Impact/Access:     Denial of Service -- Existing Account
Resolution:        Patch/Upgrade
CVE Names:         CVE-2011-0040  

Original Bulletin: 

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Microsoft Security Bulletin MS11-005 - Important

Vulnerability in Active Directory Could Allow Denial of Service (2478953)

Published: February 08, 2011

Version: 1.0

General Information

Executive Summary

This security update resolves a publicly disclosed vulnerability in Active
Directory. The vulnerability could allow denial of service if an attacker
sent a specially crafted packet to an affected Active Directory server. The
attacker must have valid local administrator privileges on the domain-joined
computer in order to exploit this vulnerability.

This security update is rated Important for Active Directory on all supported
editions of 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
Active Directory server handles service principal name (SPN) update requests.

Affected Software

Windows Server 2003 Service Pack 2
Windows Server 2003 x64 Edition Service Pack 2
Windows Server 2003 with SP2 for Itanium-based Systems

Vulnerability Information

Active Directory SPN Validation Vulnerability - CVE-2011-0040

A denial of service vulnerability exists in implementations of Microsoft
Windows Active Directory due to improper validation of service principal names
(SPN), which could result in SPN collisions. When this occurs, services that
use the SPN will downgrade to NT LAN Manager (NTLM) if configured to negotiate.
Services that are not configured to negotiate will become unavailable, resulting
in a denial of service condition. An attacker who successfully exploited this
vulnerability could cause the affected system to stop responding.

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