Executive Summary

Title Microsoft Windows SMB Tree Connect Response denial of service vulnerability
NameVU#867968First vendor Publication2017-02-02
VendorVU-CERTLast vendor Modification2017-02-03
Severity (Vendor) N/ARevisionM

Security-Database Scoring CVSS v2

Cvss vector :
Cvss Base ScoreN/AAttack RangeN/A
Cvss Impact ScoreN/AAttack ComplexityN/A
Cvss Expoit ScoreN/AAuthenticationN/A
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Vulnerability Note VU#867968

Microsoft Windows SMB Tree Connect Response denial of service vulnerability

Original Release date: 02 Feb 2017 | Last revised: 03 Feb 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.


The CERT/CC is currently unaware of a practical solution to this problem. Please consider the following 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 Updated
Microsoft CorporationAffected01 Feb 201702 Feb 2017
If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)



  • https://github.com/lgandx/PoC/tree/master/SMBv3%20Tree%20Connect
  • https://msdn.microsoft.com/en-us/library/cc246499.aspx
  • https://www.us-cert.gov/ncas/current-activity/2017/01/16/SMB-Security-Best-Practices


This vulnerability was publicly reported by PythonResponder.

This document was written by Will Dormann.

Other Information

  • CVE IDs:CVE-2017-0016
  • Date Public:01 Feb 2017
  • Date First Published:02 Feb 2017
  • Date Last Updated:03 Feb 2017
  • Document Revision:22


If you have feedback, comments, or additional information about this vulnerability, please send us email.

Original Source

Url : http://www.kb.cert.org/vuls/id/867968

Alert History

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2017-02-03 21:23:39
  • Multiple Updates
2017-02-02 21:21:13
  • First insertion