Patch tracker / CVE reference / CVE-2025-21307

CVE-2025-21307

CVE-2025-21307 is a Microsoft vulnerability that Microsoft rates Critical, with a CVSS score of 9.8 (Critical). 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.

Our data comes from Microsoft, CISA and other public sources, and it can be wrong or out of date. If you are unsure, check the linked source before you act, and tell us when we are wrong so we can fix it.

Microsoft rates it Critical. CVSS 9.8 (Critical). Fixed by 14 Microsoft security updates.

Senserva AI read on CVE-2025-21307Official patches for CVE-2025-21307Change historyAdmin questions

Risk summary

Critical
9.8
CVSS v3
1.9%
EPSS, 30 days
Critical
Severity

Not in the CISA KEV catalog. EPSS exploit probability 1.9%. CVSS 9.8 (Critical).

This CVE is among the top 10% of tracked Microsoft CVEs by EPSS exploit probability.

Senserva AI Opinion for CVE-2025-21307

This Critical Severity (CVSS 9.8) Remote Code Execution flaw sits in the Reliable Multicast Transport Driver (RMCAST), and its 81% EPSS deserves a caveat: the driver is only reachable when a program is actually listening on a Windows PGM socket, which most environments never do. Affected platforms are Windows 10 1809 and Windows Server 2019. The risk concentrates in niche setups using multicast messaging middleware.

Do this: Patch broadly per the normal wave, but first check whether any server runs software listening on PGM ports and fast-track those hosts.

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

Schedule normally
No exploitation observed as of 2026-11-03: not in the CISA KEV catalog, EPSS 2%.
Fixed by KB5049981 and 13 more (by build, listed below). Download from the Microsoft Update Catalog, or deploy via Windows Update, Intune, or WSUS.
Do this now: Deploy with your normal update cycle. This page refreshes daily; the verdict changes the day the data does.
Senserva AI Opinion and rich prompt for CVE-2025-21307

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

Official patch(es) for CVE-2025-21307

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 KB5049981, KB5049983, KB5049984, KB5049993, KB5050004, KB5050006, KB5050008, KB5050009, KB5050013, KB5050021, KB5050048, KB5050049, KB5050061, KB5050063 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-2025-21307. 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.

KB5049981KB5049983KB5049984KB5049993KB5050004KB5050006KB5050008KB5050009KB5050013KB5050021KB5050048KB5050049KB5050061KB5050063

Scope and sources

Affected products
Fixed by the same updates
CVE-2025-21333CVE-2025-21334CVE-2025-21335CVE-2025-21298CVE-2025-21311CVE-2025-21176CVE-2025-21223CVE-2025-21233
Authoritative references
Official CVE record (cve.org)NVD detailMicrosoft MSRCFIRST.org EPSS

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

New to a term on this page? CVE, KB, KEV, CVSS, and EPSS are each explained once, on the Senserva security lexicon. Reference: Microsoft CVE and vulnerability management and the Microsoft patching guide.
All information provided as is, without warranty; verify against the vendor advisory before acting. All information and usage is subject to the Senserva EULA. Data notice and terms.