Microsoft Win32k: privilege escalation flaw under attack

What is affected

Microsoft Win32k is found on ordinary personal computers and phones, so this is not only a problem for companies. If you use it and have not updated since the fix was released, you are exposed.

Microsoft Win32k contains an unspecified vulnerability that allows for privilege escalation.

What an attacker can do

This is a privilege escalation flaw. It lets an attacker turn limited access into full administrator control. Attackers pair it with another flaw or a malicious file: once anything of theirs runs on the device, this bug lets it take over completely.

How it is reached

Needs access to the device or a file opened on it

Access the attacker needs

No account needed

Does the victim have to do something?

Yes, the victim must open or click something

What to do

1. Update Microsoft Win32k now. Open the update or "About" screen, install whatever is offered and restart the app or device, because the fix is not active until you do.
2. Turn on automatic updates so the next fix arrives without you having to look for it.
3. If your device is too old to receive this update, stop using the affected app for anything sensitive and plan a replacement.

Apply updates per vendor instructions.

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on May 4, 2022, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by May 25, 2022, a deadline that has already passed. That deadline does not bind anyone else, but it shows how seriously the agency rates it.

The EPSS model estimates a 87% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 99.7% of all scored vulnerabilities.

Its CVSS severity score is 7.8 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

win32k.sys in the kernel-mode drivers in Microsoft Windows Server 2003 SP2, Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and R2, and Windows RT Gold and 8.1 allows local users to gain privileges via a crafted application, as exploited in the wild in October 2014, aka "Win32k.sys Elevation of Privilege Vulnerability."