United States Computer Emergency Readiness (US-CERT) published a new zero-day which affects its operations Microsoft Windows 8, 10 and Server.
US-CERT states:
Microsoft Windows contains a memory corruption bug in handling SMB traffic, which can allow a remote intruder without authentication to cause service denial or potentially run arbitrary code on a vulnerable system.
Attackers using this particular Zero-Day can cause denial of attacks service (DoS) against versions of Windows containing the bug. So vulnerable devices can connect to malicious SMB. US-CERT states that there is a possibility that the vulnerability could also be exploited to execute arbitrary code with Windows Core privileges.
The vulnerability description reports additional information:
Windows fails to properly handle traffic from a malicious server. In particular, Windows does not correctly handle a server response that contains too many bytes following the structure defined by the SMB2 TREE_CONNECT Response. With the connection on a malicious SMB server, the vulnerable Windows system may show BSOD (Blue Screen of Death) with Mrxsmb20.sys error. It is unclear at this point whether this vulnerability can be exploited beyond a denial-of-service attack. We have confirmed the crash with fully patched Windows 10 and Windows 8.1 client systems.
US-CERT has confirmed vulnerability to fully repaired Windows 8.1 and Windows 10 client systems. The Bleeping Computer website reports that PythonResponder security researcher claims that vulnerability also affects Windows Server 2012 and 2016.
There is currently no official confirmation that Windows Servers are affected by the vulnerability.
US-CERT ranks the vulnerability at the highest severity score (10), and it's worth noting that Microsoft has not released any information security still.
US-CERT, on the other hand, recommends blocking all outgoing SMB connections on the TCP port 139 and 445, and UDP 137 and 138 from the local WAN network.
To find out if the version of Windows that usesIf you have any SMB connections, do the following:
- In search, type Powershell, right-click the icon and open as administrator.
- Confirm the UAC to appear
- and run the Get-SmbConnection command.
