Vulnerability Note VU#867968
Microsoft Windows SMB Tree Connect Response denial of service vulnerability
Original Release date: 02 Feb 2017 | Last revised: 17 Mar 2017
Microsoft Windows contains a memory corruption bug in the handling of SMB traffic, which may allow a remote, unauthenticated attacker to cause a denial of service on a vulnerable system.
Microsoft Windows fails to properly handle traffic from a malicious server.
In particular, Windows fails to properly handle a specially-crafted server response that contains too many bytes following the structure defined in the SMB2 TREE_CONNECT Response structure.
By connecting to a malicious SMB server, a vulnerable Windows client system may crash (BSOD) in mrxsmb20.sys. We have confirmed the crash with fully-patched Windows 10 and Windows 8.1 client systems, as well as the server equivalents of these platforms, Windows Server 2016 and Windows Server 2012 R2.
Note that there are a number of techniques that can be used to trigger a Windows system to connect to an SMB share.
Some may require little to no user interaction.
Exploit code for this vulnerability is publicly available.
By causing a Windows system to connect to a malicious SMB share, a remote attacker may be able to cause a denial of service by crashing Windows.
Apply an update
This issue is addressed in Microsoft Security Bulletin MS17-012. Please also consider the following best practices, which also function as workarounds:
Block outbound SMB
Consider blocking outbound SMB connections (TCP ports 139 and 445 along with UDP ports 137 and 138) from the local network to the WAN.
Vendor Information (Learn More)
VendorStatusDate NotifiedDate UpdatedMicrosoft CorporationAffected01 Feb 201717 Mar 2017If you are a vendor and your product is affected, let
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This vulnerability was publicly reported by PythonResponder.
This document was written by Will Dormann.
01 Feb 2017
Date First Published:
02 Feb 2017
Date Last Updated:
17 Mar 2017
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