Patch tracker / CVE reference / CVE-2025-21191

CVE-2025-21191

CVE-2025-21191 is a high severity Microsoft vulnerability with a CVSS score of 7.0. Its EPSS score puts the probability of exploitation in the next 30 days at 14%. Microsoft has shipped the fix: deploy one of the 14 updates below from the Microsoft Update Catalog, and see where this CVE sits against the rest on the patch tracker.

Risk summary

High

7.0

CVSS

14%

EPSS, 30 days

High

Severity

Not in the CISA KEV catalog. EPSS exploit probability 14%. CVSS 7.0 (High).

This CVE is among the lower half of tracked Microsoft CVEs by EPSS exploit probability.

Senserva AI Opinion for CVE-2025-21191

A second LSA elevation of privilege bug this batch reaches the newer Server 2025 alongside the legacy Windows 10 1809, showing the authentication subsystem issue spans both current and older Windows builds. As with the other LSA CVE, the sensitivity of LSA as a credential-handling process makes this worth treating seriously despite the moderate 18 percent EPSS.

Do this: Patch Server 2025 domain controllers and Windows 10 1809 systems together; both carry distinct LSA CVEs this cycle.

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

Senserva AI Opinion and rich prompt for CVE-2025-21191

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-2025-21191 (source: https://senserva.com/cve/CVE-2025-21191.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- CVE-2025-21191: High severity Microsoft vulnerability, CVSS 7.0
- EPSS 30-day exploitation probability: 14%
- Actively exploited (CISA KEV): no
- Fixed by: KB5055518, KB5055519, KB5055521, KB5055523, KB5055526, KB5055527, KB5055528, KB5055547, KB5055557, KB5055561, KB5055570, KB5055581, KB5055596, KB5055609
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 this cycle

Not confirmed exploited yet, but the 30-day exploit probability is high (EPSS 14%).

Fixed by KB5055518 and 13 more (by build, listed below). Download from the Microsoft Update Catalog, or deploy via Windows Update, Intune, or WSUS.

Do this now: Patch in this maintenance window; do not let it slip to the next one.

Official patch(es) for CVE-2025-21191

Elevated priority: high severity or a meaningful exploitation probability, sooner if an affected product is internet-facing. In Intune or Defender, confirm whether the fixing updates KB5055518, KB5055519, KB5055521, KB5055523, KB5055526, KB5055527, KB5055528, KB5055547, KB5055557, KB5055561, KB5055570, KB5055581, KB5055596, KB5055609 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-2025-21191. 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.

KB5055518 KB5055519 KB5055521 KB5055523 KB5055526 KB5055527 KB5055528 KB5055547 KB5055557 KB5055561 KB5055570 KB5055581 KB5055596 KB5055609

Scope and sources

Affected products

Fixed by the same updates

CVE-2025-29824 CVE-2025-21205 CVE-2025-21221 CVE-2025-21222 CVE-2025-26647 CVE-2025-26669 CVE-2025-27477 CVE-2025-27481

Authoritative references

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

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