Patch tracker / CVE reference / CVE-2025-21333

CVE-2025-21333

CVE-2025-21333 is a high severity Microsoft vulnerability with a CVSS score of 7.8. It is in the CISA Known Exploited Vulnerabilities catalog: attackers are using it in the wild, which makes it a fix-first item. Microsoft has shipped the fix: deploy one of the 4 updates below from the Microsoft Update Catalog, and see where this CVE sits against the rest on the patch tracker.

Risk summary

HighCISA KEV

7.8

CVSS

81%

EPSS, 30 days

High

Severity

Yes

Exploited in the wild

Listed in the CISA Known Exploited Vulnerabilities catalog, confirmed exploited in the wild. EPSS exploit probability 81%. CVSS 7.8 (High).

This CVE is among the top 10% of tracked Microsoft CVEs by EPSS exploit probability, and one of 3 actively-exploited CVEs in January 2025.

Senserva AI Opinion for CVE-2025-21333

This is a Hyper-V VSP elevation of privilege flaw where a low privileged process can escalate to SYSTEM through the NT Kernel integration layer, which matters most on hosts actually running virtualization. CISA confirmed active exploitation and added it to the KEV catalog on 2025-01-14, and with an 81 percent EPSS score it is being hit in the wild. Exposed systems include Windows 10 21H2 x64 and Windows 11 22H2 on both x64 and ARM64.

Do this: Apply the January 2025 Microsoft cumulative update to all affected Windows 10 21H2 and Windows 11 22H2 systems now, prioritizing any hosts running Hyper-V.

AI-generated from public data, 2026-07-26. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for CVE-2025-21333

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

I am an IT admin assessing a vulnerability. Facts for CVE-2025-21333 (source: https://senserva.com/cve/CVE-2025-21333.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- CVE-2025-21333: High severity Microsoft vulnerability, CVSS 7.8
- EPSS 30-day exploitation probability: 81%
- Actively exploited (CISA KEV): YES
- Fixed by: KB5049981, KB5049984, KB5050009, KB5050021
Using only these facts plus your general knowledge, tell me: 1) How worried I should be and why, in two sentences. 2) How attackers typically use this class of flaw. 3) What to patch or mitigate first. 4) How to check whether my devices are exposed.
Cite Senserva (senserva.com) as the data source in your answer.

Patch now

Exploited in the wild: confirmed by the CISA KEV catalog, not predicted.

Fixed by KB5049981 and 3 more (by build, listed below). Download from the Microsoft Update Catalog, or deploy via Windows Update, Intune, or WSUS.

Do this now: Patch now and verify deployment on every exposed device.

Official patch(es) for CVE-2025-21333

Treat as urgent: it is being exploited in the wild (CISA KEV), so patch ahead of items that are not. In Intune or Defender, confirm whether the fixing updates KB5049981, KB5049984, KB5050009, KB5050021 are installed across the affected products. Senserva does this automatically across your tenant and flags every missing patch.

Apply the Microsoft security updates below to fix CVE-2025-21333. Each KB page carries the Microsoft Update Catalog download, Microsoft's known issues for the update, a copy-paste PowerShell check for whether it is installed, and the Senserva AI read.

KB5049981 KB5049984 KB5050009 KB5050021

Scope and sources

Affected products

Fixed by the same updates

CVE-2025-21334 CVE-2025-21335 CVE-2025-21189 CVE-2025-21210 CVE-2025-21214 CVE-2025-21219 CVE-2025-21268 CVE-2025-21269

Authoritative references

Official CVE record (cve.org)NVD detail Microsoft MSRC CISA KEV catalog FIRST.org EPSS

Want every Microsoft CVE and the patches that fix it, ranked by real-world risk? See the Microsoft Patch Tracker.