Microsoft Security Bulletin MS15-133 - Important

Security Update for Windows PGM to Address Elevation of Privilege (3116130)

Published: December 8, 2015

Version: 1.0

Executive Summary

This security update resolves a vulnerability in Microsoft Windows. The vulnerability could allow elevation of privilege if an attacker logs on to a target system and runs a specially crafted application that, by way of a race condition, results in references to memory locations that have already been freed. Microsoft Message Queuing (MSMQ) must be installed and the Windows Pragmatic General Multicast (PGM) protocol specifically enabled for a system to be vulnerable. MSMQ is not present in default configurations and, if it is installed, the PGM protocol is available but disabled by default.

This security update is rated Important for all supported releases of Microsoft Windows. For more information, see the Affected Software section.

The security update addresses the vulnerability by deferring memory cleanup until the contents of memory no longer need to be accessed. For more information about the vulnerability, see the Vulnerability Information section.

For more information about this update, see Microsoft Knowledge Base Article 3116130.

Affected Software and Vulnerability Severity Ratings

The following software versions or editions are affected. Versions or editions that are not listed are either past their support life cycle or are not affected. To determine the support life cycle for your software version or edition, see Microsoft Support Lifecycle.

The severity ratings indicated for each affected software assume the potential maximum impact of the vulnerability. For information regarding the likelihood, within 30 days of this security bulletin’s release, of the exploitability of the vulnerability in relation to its severity rating and security impact, please see the Exploitability Index in the December bulletin summary.

^[1]This update is only available via Windows Update.

^[2]Windows 10 updates are cumulative. In addition to containing non-security updates, they also contain all of the security fixes for all of the Windows 10-affected vulnerabilities shipping with the monthly security release. The update is available via the Windows Update Catalog.

Note Windows Server Technical Preview 3 and Windows Server Technical Preview 4 are affected. Customers running these operating systems are encouraged to apply the update, which is available via Windows Update.

Vulnerability Information

Windows PGM UAF Elevation of Privilege Vulnerability - CVE-2015-6126

An elevation of privilege vulnerability exists in the Windows Pragmatic General Multicast (PGM) protocol that is caused when an attacker-induced race condition results in references to memory contents that have already been freed. An attacker who successfully exploited this vulnerability could execute code with elevated privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

To exploit this vulnerability, an attacker would first have to log on to the target system. An attacker could then run a specially crafted application that is designed to create the race condition that leads to elevated privileges. The security update addresses the vulnerability by deferring memory cleanup until the contents of memory no longer need to be accessed.

Microsoft received information about this vulnerability through coordinated vulnerability disclosure. At the time this security bulletin was originally issued, Microsoft was unaware of any attack attempting to exploit this vulnerability.

Mitigating Factors

The following mitigating factors may be helpful in your situation:

• Microsoft Message Queuing (MSMQ) must be installed and PGM specifically enabled for a system to be vulnerable. MSMQ is not present in default configurations and if it is installed the PGM protocol is available but disabled by default.

Workarounds

Microsoft has not identified any workarounds for this vulnerability.

Security Update Deployment

For Security Update Deployment information, see the Microsoft Knowledge Base article referenced here in the Executive Summary.

Acknowledgments

Microsoft recognizes the efforts of those in the security community who help us protect customers through coordinated vulnerability disclosure. See Acknowledgments for more information.

Disclaimer

The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

Revisions

• V1.0 (December 8, 2015): Bulletin published.

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