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What is CVE-2025-21333?A high-severity flaw criminals are using now.

High severityKnown exploited7 affected products
The short answer

CVE-2025-21333 is a high-severity flaw (CVSS 7.8) in Windows 10 21H2 from Microsoft, published on 14 January 2025. It is on the list of flaws known to be exploited, so criminals are already using it. The latest forecast puts its chance of use in the next 30 days at 10.0%. If you run an affected version, patch it first.

Check if it affects you →How to fix it

Published 14 January 2025. Record last updated 3 April 2025. We keep this page's data up to date.

What it does

What is CVE-2025-21333? In plain terms.

An attacker has to be already on the device with an ordinary user account, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.

The official description

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

What kind of flaw is it?

  • CWE-122Heap-based Buffer Overflow
CVSS 3.1 scoreHigh · 7.8

How an attack on it works

Read straight from its severity rating, translated out of the shorthand.

  • Where an attacker can beAlready on the device
  • How hard it is to pull offEasy: no special conditions
  • Login needed firstAn ordinary user account
  • Does someone have to clickNo, nobody has to do anything
  • What an attacker getsCan read data, change data and take it offline

Severity vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Exploitation

Is CVE-2025-21333 being exploited? Yes.

Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at 10.0%.

Known to be exploitedYesOn the government list of exploited flaws
Chance of use in the next 30 days10.0%Its EPSS score, from the latest forecast

Timeline

  1. Published
  2. Record last updated
  3. Exploit likelihood fell
How Precursor Intelligence ranks it
74out of 100High

CVE-2025-21333 scores 74. Action: Emergency patch.

We keep the score of every published flaw up to date as the evidence changes. Four things go into the score, and evidence that criminals are actually using it counts most. In order:

  • Evidence it is being exploitedBiggest factor
  • How severe it isStrong factor
  • How widely exposed it isSmaller factor
  • Threat activity around itSmaller factor

85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score.

When CVE-2025-21333 matches software you track, it lands in your list with its score and the reasons behind it.

See your own ranked list →
Affected products

Who is affected by CVE-2025-21333? 7 products.

The published record lists 7 products from 1 vendor. Versions are shown as published: "before 10.0.19044.5371" means every version up to, but not including, 10.0.19044.5371. If you run one of these, check your version, then go to the fix below.

Remediation

How do I fix CVE-2025-21333? Four steps.

  1. Check whether you run itCompare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
  2. Apply the vendor’s fixInstall the update named in the vendor’s advisory. We’ve put the advisories and patch notes first in the list.
  3. If you can’t patch todayFollow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
  4. Check it wasn’t used before you patchedBecause criminals are already using this flaw, look for signs of a break-in on affected systems using the vendor’s guidance.

References

3 links
Precursor Intelligence

Does CVE-2025-21333 affect you? We'll keep checking.

Looking flaws up one at a time doesn't scale. Tell us what you run once, and we tell you which flaws matter to you, in what order, and keep watching for new ones.

  1. Tell us what you runPick your software from a list, or let us work it out from your website.
  2. We match it to every flawOver 400,000 published flaws, checked against your list.
  3. Ranked by real-world riskA 0 to 100 score, led by evidence criminals are using it.
  4. Told as soon as we knowAn alert by email, in the app or by webhook to your own tools.
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FAQ

Common questions, answered plainly.

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CVE-2025-21333 is a high-severity flaw in Windows 10 21H2 from Microsoft, published on 14 January 2025. An attacker has to be already on the device with an ordinary user account, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.

It scores 7.8 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2025-21333 is 74 out of 100, which is High. Its action is "Emergency patch". Attackers are using this flaw today. If you run an affected version, it goes to the top of your list.

Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at 10.0%.

For Windows 10 21H2 from Microsoft: before 10.0.19044.5371. The record lists 7 products in all, each with its versions, under "Who is affected" on this page.

Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet. Because criminals are already using it, also check affected systems for signs of a break-in.

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