Microsoft Security Bulletin MS15-028 - Important

Vulnerability in Windows Task Scheduler Could Allow Security Feature Bypass (3030377)

Published: March 10, 2015

Version: 1.0

Executive Summary

This security update resolves a vulnerability in Microsoft Windows. The vulnerability could allow a user with limited privileges on an affected system to leverage Task Scheduler to execute files that they do not have permissions to run. An attacker who successfully exploited this vulnerability could bypass access control list (ACL) checks and run privileged executables.

This security update is rated Important for all supported editions of Windows 7, Windows Server 2008 R2, Windows 8, Windows Server 2012, Windows RT, Windows 8.1, Windows Server 2012 R2, and Windows RT 8.1. For more information, see the Affected Software section.

The security update addresses the vulnerability by correcting how Task Scheduler validates impersonation levels. For more information about the vulnerability, see the Vulnerability Information section.

For more information about this update, see Microsoft Knowledge Base Article 3030377.

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 7
Windows 7 for 32-bit Systems Service Pack 1
(3030377)
Security Feature Bypass Important None
Windows 7 for x64-based Systems Service Pack 1
(3030377)
Security Feature Bypass Important None
Windows Server 2008 R2
Windows Server 2008 R2 for x64-based Systems Service Pack 1
(3030377)
Security Feature Bypass Important None
Windows Server 2008 R2 for Itanium-based Systems Service Pack 1
(3030377)
Security Feature Bypass Important None
Windows 8 and Windows 8.1
Windows 8 for 32-bit Systems
(3030377)
Security Feature Bypass Important None
Windows 8 for x64-based Systems
(3030377)
Security Feature Bypass Important None
Windows 8.1 for 32-bit Systems
(3030377)
Security Feature Bypass Important None
Windows 8.1 for x64-based Systems
(3030377)
Security Feature Bypass Important None
Windows Server 2012 and Windows Server 2012 R2
Windows Server 2012
(3030377)
Security Feature Bypass Important None
Windows Server 2012 R2
(3030377)
Security Feature Bypass Important None
Windows RT and Windows RT 8.1
Windows RT[1] (3030377) Security Feature Bypass Important None
Windows RT 8.1[1] (3030377) Security Feature Bypass Important None
Server Core installation option
Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation)
(3030377)
Security Feature Bypass Important None
Windows Server 2012 (Server Core installation)
(3030377)
Security Feature Bypass Important None
Windows Server 2012 R2 (Server Core installation)
(3030377)
Security Feature Bypass Important None

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

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 March bulletin summary.

Vulnerability Severity Rating and Maximum Security Impact by Affected Software
Affected Software Task Scheduler Security Feature Bypass Vulnerability - CVE-2015-0084 Aggregate Severity Rating
Windows 7
Windows 7 for 32-bit Systems Service Pack 1
(3030377)
Important
Security Feature Bypass
Important
Windows 7 for x64-based Systems Service Pack 1
(3030377)
Important
Security Feature Bypass
Important
Windows Server 2008 R2
Windows Server 2008 R2 for x64-based Systems Service Pack 1
(3030377)
Important
Security Feature Bypass
Important
Windows Server 2008 R2 for Itanium-based Systems Service Pack 1
(3030377)
Important
Security Feature Bypass
Important
Windows 8 and Windows 8.1
Windows 8 for 32-bit Systems
(3030377)
Important
Security Feature Bypass
Important
Windows 8 for x64-based Systems
(3030377)
Important
Security Feature Bypass
Important
Windows 8.1 for 32-bit Systems
(3030377)
Important
Security Feature Bypass
Important
Windows 8.1 for x64-based Systems
(3030377)
Important
Security Feature Bypass
Important
Windows Server 2012 and Windows Server 2012 R2
Windows Server 2012
(3030377)
Important
Security Feature Bypass
Important
Windows Server 2012 R2
(3030377)
Important
Security Feature Bypass
Important
Windows RT and Windows RT 8.1
Windows RT
(3030377)
Important
Security Feature Bypass
Important
Windows RT 8.1
(3030377)
Important
Security Feature Bypass
Important
Server Core installation option
Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation)
(3030377)
Important
Security Feature Bypass
Important
Windows Server 2012 (Server Core installation)
(3030377)
Important
Security Feature Bypass
Important
Windows Server 2012 R2 (Server Core installation)
(3030377)
Important
Security Feature Bypass
Important

Vulnerability Information

Task Scheduler Security Feature Bypass Vulnerability - CVE-2015-0084

A security feature bypass vulnerability exists when Windows Task Scheduler fails to properly validate and enforce impersonation levels. The vulnerability could allow a user with limited privileges on an affected system to leverage Task Scheduler to execute files that they do not have permissions to run.

An attacker who successfully exploited this vulnerability could bypass ACL checks and run privileged executables. The update addresses the vulnerability by correcting how Task Scheduler validates impersonation levels.

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

Microsoft has not identified any mitigating factors for this vulnerability.

Workarounds

The following workarounds may be helpful in your situation:

  • Turn off the Task Scheduler service
    Note Modifying the Registry incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from incorrect modification of the Registry can be solved. Modify the Registry at your own risk.

    1. Open Registry Editor and navigate to HKLM\SYSTEM\CurrentControlSet\Services\Schedule
    2. Change the value of the Start key from 2 to 4 (disabled).
    3. Restart the system.

Impact of workaround. Scheduled tasks will no longer run.

How to undo the workaround.

  1. Open Registry Editor and navigate to HKLM\SYSTEM\CurrentControlSet\Services\Schedule
  2. Change the value of the Start key from 4 to 2 (enabled).
  3. Restart the system.

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 (March 10, 2015): Bulletin published.

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