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. |
Vendor Information (Learn More)
| Vendor | Status | Date Notified | Date Updated |
|---|
| Microsoft Corporation | Affected | 01 Feb 2017 | 02 Feb 2017 |
| Group | Score | Vector |
|---|
| Base | 7.8 | AV:N/AC:L/Au:N/C:N/I:N/A:C |
| Temporal | 7.0 | E:POC/RL:U/RC:C |
| Environmental | 7.0 | CDP:ND/TD:H/CR:ND/IR:ND/AR:ND |
References