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Actively exploited vulnerability

Microsoft Win32k: memory corruption flaw under attack

CVE-2015-2546 · Microsoft Win32k Memory Corruption Vulnerability

Concerns everyone who uses it8.2 highUsed in ransomware attacks

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.

The kernel-mode driver in Microsoft Windows OS and Server allows local users to gain privileges via a crafted application.

CISA's description

What an attacker can do

This is a memory corruption flaw. It lets an attacker corrupt the program's memory by feeding it specially crafted content: a web page, a file or a network message. The result ranges from a crash to the attacker running their own code.

How it is reached
Needs access to the device or a file opened on it
Access the attacker needs
A basic user account
Does the victim have to do something?
Yes, the victim must open or click something

CISA records this vulnerability as known to be used in ransomware campaigns: attackers use it to get in, then encrypt files and demand payment.

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.

Action required by CISA for US federal agencies

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on March 15, 2022, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by April 5, 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 10% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 96% of all scored vulnerabilities.

Its CVSS severity score is 8.2 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

The kernel-mode driver in Microsoft Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and R2, Windows RT Gold and 8.1, and Windows 10 allows local users to gain privileges via a crafted application, aka "Win32k Memory Corruption Elevation of Privilege Vulnerability," a different vulnerability than CVE-2015-2511, CVE-2015-2517, and CVE-2015-2518.

NIST National Vulnerability Database
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