Microsoft Security Bulletin MS16-114 - Important

Security Update for Windows SMBv1 Server (3185879)

Published: September 13, 2016

Version: 1.0

Executive Summary

This security update resolves a vulnerability in Microsoft Windows. On Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2 operating systems, the vulnerability could allow remote code execution if an authenticated attacker sends specially crafted packets to an affected Microsoft Server Message Block 1.0 (SMBv1) Server. The vulnerability does not impact other SMB Server versions. Although later operating systems are affected, the potential impact is denial of service.

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

The security update addresses the vulnerability by correcting how the Microsoft SMBv1 Server handles specially crafted requests. For more information about the vulnerability, see the Vulnerability Information section.

For more information about this update, see Microsoft Knowledge Base Article 3185879.

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 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.

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

^[2]Windows 10 updates are cumulative. The monthly security release includes all security fixes for vulnerabilities that affect Windows 10, in addition to non-security updates. The update is available via the Windows Update Catalog.

Note The vulnerability discussed in this bulletin affects Windows Server 2016 Technical Preview 5. To be protected from the vulnerability, Microsoft recommends that customers running this operating system apply the current update, which is available from Windows Update. 

*The Updates Replaced column shows only the latest update in any chain of superseded updates. For a comprehensive list of updates replaced, go to the Microsoft Update Catalog, search for the update KB number, and then view update details (updates replaced information is provided on the Package Details tab).

Vulnerability Information

Windows SMB Authenticated Remote Code Execution Vulnerability - CVE-2016-3345

For Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2 operating systems a remote code execution vulnerability exists in the way that the Microsoft Server Message Block 1.0 (SMBv1) Server handles certain requests when an authenticated attacker sends specially crafted packets to the SMBv1 server. The vulnerability does not impact other SMB Server versions.

On later operating systems an attacker who successfully exploited this vulnerability could cause the affected system to stop responding until it is manually restarted.

To exploit the vulnerability an attacker would first need to authenticate to the SMBv1 Server and have permission to open files on the target server before attempting the attack.

The security update addresses the vulnerability by correcting how the Microsoft SMBv1 Server handles specially crafted requests.

The following table contains links to the standard entry for each vulnerability in the Common Vulnerabilities and Exposures list:

Mitigating Factors

The following mitigating factors may be helpful in your situation:

• To exploit this vulnerability, an attacker must be able to establish an authenticated SMBv1 session to the SMBv1 Server.

Workarounds

The following workarounds may be helpful in your situation:

• Disable SMBv1

For customers running Windows Vista and later

See Microsoft Knowledge Base Article 2696547.

Alternative method for customers running Windows 8.1 or Windows Server 2012 R2 and later

For client operating systems:

1. Open Control Panel, click Programs, and then click Turn Windows features on or off.
2. In the Windows Features window, clear the SMB1.0/CIFS File Sharing Support checkbox, and then click OK to close the window.
3. Restart the system.
    

For server operating systems:

1. Open Server Manager and then click the Manage menu and select Remove Roles and Features.
2. In the Features window, clear the SMB1.0/CIFS File Sharing Support checkbox, and then click OK to close the window.
3. Restart the system.
    

Impact of workaround. The SMBv1 protocol will be disabled on the target system.

How to undo the workaround. Retrace the workaround steps, instead restoring the SMB1.0/CIFS File Sharing Support feature to an active state.

FAQ

What versions of SMB are impacted by this vulnerability?
This vulnerability affects only SMBv1.

What is the difference between SMBv1 and SMBv2? 
Both protocols are used by clients to request file and print services from a server system over the network. Both are stateful protocols in which clients establish a connection to a server, establish an authenticated context on that connection, and then issue a variety of requests to access files, printers, and named pipes for interprocess communication. The SMBv2 protocol is a major revision of the existing SMB protocol. While many of the underlying concepts are the same, the packet formats are completely different. In addition to providing all of the capabilities found in SMBv1, the SMBv2 protocol provides several enhancements:

• Allowing an open to a file to be reestablished after a client connection becomes temporarily disconnected.
• Allowing the server to balance the number of simultaneous operations that a client can have outstanding at any time.
• Providing scalability in terms of the number of shares, users, and simultaneously open files.
• Supporting symbolic links.
• Using a stronger algorithm to validate the integrity of requests and responses.

Security Update Deployment

For Security Update Deployment information, see the Microsoft Knowledge Base article referenced 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 (September 13, 2016): Bulletin published.

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