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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
Overview
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.
Description
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.
Impact
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.
Solution
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.
https://www.kb.cert.org/vuls/id/867968
Microsoft Windows SMB Tree Connect Response denial of service vulnerability
Original Release date: 02 Feb 2017 | Last revised: 03 Feb 2017
Overview
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.
Description
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.
Impact
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.
Solution
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.
https://www.kb.cert.org/vuls/id/867968