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Actively exploited vulnerability

Microsoft Windows: memory corruption flaw under attack

CVE-2025-21335 · Microsoft Windows Hyper-V NT Kernel Integration VSP Use-After-Free Vulnerability

Concerns everyone who uses it7.8 high

What is affected

Microsoft Windows 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 Windows Hyper-V NT Kernel Integration VSP contains a use-after-free vulnerability that allows a local attacker to gain SYSTEM privileges.

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?
No, works without the victim doing anything

What to do

  1. Update Microsoft Windows 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 mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

Action required by CISA for US federal agencies

Vendor advisories and fixes

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on January 14, 2025, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by February 4, 2025, 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 1.4% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 71% 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

Windows Hyper-V NT Kernel Integration VSP Elevation of Privilege Vulnerability

NIST National Vulnerability Database
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