14 DAY TRIAL // Microsoft suggested in a statement that a fix for the recently-disclosed zero-day flaw affecting several Windows versions would only be shipped on this month’s Patch Tuesday, even though users might already be under attack.
Microsoft explains that this vulnerability is considered to be “low risk,” which means that an out-of-band patch wouldn’t be released, with the company waiting for the Patch Tuesday cycle to fix the vulnerability. This month, Patch Tuesday takes place on February 14.
“Windows is the only platform with a customer commitment to investigate reported security issues, and proactively update impacted devices as soon as possible. Our standard policy is that on issues of low risk, we remediate that risk via our current Update Tuesday schedule,” a company spokesperson said.
One of the reasons Microsoft doesn’t want to ship an out-of-band patch is that it would trigger a reboot of all systems, and given the fact that the vulnerability is said to affect Windows 10, Windows 8.1, Windows Server 2016, and Windows Server 2012 R2, the impact would be quite major.
No workaround just yet
In an advisory posted on the Carnegie Mellon University CERT website, users are warned that a zero-day flaw in the SMB network file sharing protocol can be used by cybercriminals to launch denial of service attacks against vulnerable computers eventually crashing them with a BSOD.
Furthermore, there were warnings that attacks could also gain arbitrary code execution capabilities with a successful exploit, and this would fully compromise a system unless a patch is provided.
“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,” security experts warned last week, explaining that they successfully reproduced the bug.
There is no workaround at the time being, but the CERT says that blocking outbound SMB connections (TCP ports 139 and 445 along with UDP ports 137 and 138) from the local network to the WAN could be an easy way to prevent exploits until a patch is delivered.