Microsoft Security Bulletin MS15-105 - Important

Vulnerability in Windows Hyper-V Could Allow Security Feature Bypass (3091287)

Published: September 8, 2015

Version: 1.0

Executive Summary

This security update resolves a vulnerability in Microsoft Windows. The vulnerability could allow security feature bypass if an attacker runs a specially crafted application that could cause Windows Hyper-V to incorrectly apply access control list (ACL) configuration settings. Customers who have not enabled the Hyper-V role are not affected.

This security update is rated Important for all supported editions of Windows 8.1 for x64-based Systems, Windows Server 2012 R2, and Windows 10 for x64-based Systems. For more information, see the Affected Software section.

The security update addresses the vulnerability by correcting how Hyper-V applies ACL configuration settings. For more information about the vulnerability, see the Vulnerability Information section.

For more information about this update, see Microsoft Knowledge Base Article 3091287.

Affected Software

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.

|**Operating System**|**Maximum Security Impact**|**Aggregate Severity Rating**|**Updates Replaced**| |------------|------------|------------|------------| |**Windows 8.1**| |[Windows 8.1 for x64-based Systems]( (3087088)|Security Feature Bypass|Important|None| |**Windows Server 2012 R2**| |[Windows Server 2012 R2]( (3087088)|Security Feature Bypass|Important|None| |**Windows 10**| |[Windows 10 for x64-based Systems]([1](3081455)|Security Feature Bypass|Important|[3081444](| |**Server Core installation option**| |[Windows Server 2012 R2]( (Server Core installation) (3087088)|Security Feature Bypass|Important|None|

[1]The Windows 10 update is cumulative. In addition to containing non-security updates, it also contains all of the security fixes for all of the Windows 10-affected vulnerabilities shipping with this month’s security release. See Microsoft Knowledge Base Article 3081444 for more information and download links. 

Note Windows Server Technical Preview 2 and Windows Server Technical Preview 3 are affected. Customers running this operating system are encouraged to apply the update, which is available via Windows Update.

Update FAQ

I do not have Hyper-V enabled, why am I being offered this update?
The vulnerable code exists in the affected software that is listed in the affected software table. As a defense-in-depth measure, and to ensure that systems are protected if Hyper-V were to be enabled, the update is considered to be applicable to all supported products and versions that contain the vulnerable code.

Severity Ratings and Vulnerability Identifiers

The following severity ratings 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 September bulletin summary.

|**Vulnerability Severity Rating and Maximum Security Impact by Affected Software**| |------------| |**Affected Software**|[**Hyper-V Security Feature Bypass Vulnerability - CVE-2015-2534**](|**Aggregate Severity Rating**| |**Windows 8.1**| |Windows 8.1 for x64-based Systems (3087088)|**Important**  Security Feature Bypass|**Important**| |**Windows Server 2012 R2**| |Windows Server 2012 R2 (3087088)|**Important**  Security Feature Bypass|**Important**| |**Windows 10**| |Windows 10 for x64-based Systems (3081455)|**Important**  Security Feature Bypass|**Important**| |**Server Core installation option**| |Windows Server 2012 R2 (Server Core installation) (3087088)|**Important**  Security Feature Bypass|**Important**|


Vulnerability Information

Hyper-V Security Feature Bypass Vulnerability - CVE-2015-2534

A security feature bypass vulnerability exists in Windows Hyper-V when access control list (ACL) configuration settings are not applied correctly. To exploit the vulnerability, an attacker could run a specially crafted application that could cause Hyper-V to allow unintended network traffic. Customers who have not enabled the Hyper-V role are not affected. The security update addresses the vulnerability by correcting how Hyper-V applies ACL configuration settings.

Microsoft received information about this vulnerability through coordinated vulnerability disclosure. When this security bulletin was originally issued Microsoft had not received any information to indicate that this vulnerability had been publicly used to attack customers.

Mitigating Factors

The following mitigating factors may be helpful in your situation:

  • Customers who have not enabled the Hyper-V role are not affected.


Microsoft has not identified any workarounds for this vulnerability.

Security Update Deployment

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


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


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.


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

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