Patch tracker / CVE reference / CVE-2025-21307

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CVE-2025-21307

Patch this cycle
Not confirmed exploited yet, but the 30-day exploit probability is high (EPSS 81%).
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: Patch in this maintenance window; do not let it slip to the next one.

Critical severity Microsoft vulnerability, CVSS 9.8. Fixed by 14 Microsoft security updates.

CVE-2025-21307 is a critical severity Microsoft vulnerability with a CVSS score of 9.8. Its EPSS score puts the probability of exploitation in the next 30 days at 81%. 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.

Critical

Risk summary

CVSS base
9.8
EPSS exploit probability
81%
Severity
Critical

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.

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.

Full tracking and change history for CVE-2025-21307

Published
2025-01-14
Last revised
2025-01-14
Changes tracked
1

Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.

Exploitation and severity

Not in the CISA KEV catalog. EPSS exploit probability 81%. CVSS 9.8 (Critical).

This CVE is among the top 25% of tracked Microsoft CVEs by EPSS exploit probability.

Official patch(es) for CVE-2025-21307

High priority: EPSS puts the odds of near-term exploitation high. 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 links to the Microsoft Update Catalog download for every affected product.

KB5049981KB5049983KB5049984KB5049993KB5050004KB5050006KB5050008KB5050009KB5050013KB5050021KB5050048KB5050049KB5050061KB5050063

Affected products

Common questions about CVE-2025-21307

Is CVE-2025-21307 actively exploited?

It is not currently listed in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score puts the probability of exploitation in the next 30 days at 81%.

What patch fixes CVE-2025-21307?

Microsoft fixed CVE-2025-21307 in KB5049981, KB5049983, KB5049984, KB5049993, KB5050004, KB5050006, KB5050008, KB5050009, KB5050013, KB5050021, KB5050048, KB5050049, KB5050061, KB5050063. Download from the Microsoft Update Catalog, or let Intune, Windows Update, or WSUS deliver it.

Which products are affected by CVE-2025-21307?

Windows 10 Version 1809 for 32-bit Systems, Windows 10 Version 1809 for x64-based Systems, Windows Server 2019.

Can I ask my own AI about CVE-2025-21307?

Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2025-21307's key facts: severity, CVSS, EPSS exploit probability, CISA KEV status, and the fixing KB. Copy it into Claude, ChatGPT, or Copilot for a triage plan; the data is refreshed three times a day (5 AM, 12:30 PM, and 7 PM US Central).

Fixed by the same updates

If you are patching CVE-2025-21307, the same updates also fix these:

CVE-2025-21333CVE-2025-21334CVE-2025-21335CVE-2024-49120CVE-2024-7344CVE-2025-21176CVE-2025-21189CVE-2025-21193

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.

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Most searched on Senserva right now

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Sponsored by Senserva

Siemserva by Senserva reports patch status for your own devices: which ones are exposed to CVE-2025-21307, for example, ranked by what attackers actually exploit. If this page saves you time, a link to it with a mention of Senserva helps others find it. Thank you.

  • Patch status in one scan: which devices are affected, which are not
  • Missing updates ranked by CISA KEV and EPSS, so you fix the right things first
  • Data from Intune, Microsoft Defender, Windows Autopatch, and Azure Update Manager, with more sources on the way
  • Third-party app patching too: updates published to Intune by PatchMyPC, Scappman, Robopack, or any vendor, read vendor-neutrally
  • Optional AI Enhanced Reporting: plain-language summaries and recommended next steps written into your reports
  • Then go further: 650+ security checks find the drift detection misses your last hardening pass left behind, with compliance evidence and Senserva Trustworthy AI remediation
Senserva patching for Microsoft 365
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Patching in action in two minutes. Watch page · All videos.

SenservaPATCHINGTenant: Contoso Manufacturing ▾OverviewAutopatch healthDevicesAsk SenservaExport Patch Status Report
3 actively exploited CVEs are unmitigated on devices in this tenant, per CISA KEV.View fix-first list ↓
312
Devices scanned
Intune + Autopatch + Defender
3
Exploited updates missing
CISA KEV, unmitigated
905
Microsoft updates tracked
Refreshed daily, MSRC + NVD
650+
Security checks in scan
Patch, config, identity, logs

Triage order for this list

Same order in the dashboard, the report, and every AI answer
1st · overrides everything
Actively exploited (KEV)
e.g. KB5040219, CVE-2026-31210
→
2nd · tiebreaker
Severity (Critical → Low)
MSRC + EPSS probability
→
3rd · tiebreaker
Days waiting
Oldest unresolved first

Ranked missing updates, fix-first order

27 findings · showing top 2
#UpdateCVESeveritySourceDevicesWaiting
1KB5040219
Windows 11 23H2 cumulative
CVE-2026-31210
KEV EPSS 0.94		CriticalDefender4119 daysAdd to fix-first
2KB5040088
.NET Framework security update
CVE-2026-29981
KEV		CriticalIntune1712 daysAdd to fix-first
Estimated dashboard, sample data for illustration

Ask Senserva

via Claude + MCP
Which devices are still missing the fix for CVE-2026-31210?
41 devices are missing KB5040219, which resolves CVE-2026-31210. This CVE is on CISA KEV, so CISA BOD 22-01 calls for remediation within 14 days. You are at 19 days and counting.
source: scan_db · defender_posture · kev_join, not model memory
Get Devices Found Get Devices Missing
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Lexicon: the terms on this page
CVE
Common Vulnerabilities and Exposures. A unique ID for one publicly known vulnerability, such as CVE-2025-1234.
KB
Microsoft Knowledge Base article. The identifier for a specific Microsoft update.
KEV
CISA Known Exploited Vulnerabilities. CVEs confirmed exploited in the wild. Fix these first.
CVSS
Common Vulnerability Scoring System. A standardized Severity score from 0 to 10.
EPSS
Exploit Prediction Scoring System. The probability a CVE will be exploited in the next 30 days.
MSRC
Microsoft Security Response Center. Microsoft's Patch Tuesday advisories and KB-to-CVE mapping.
NVD
National Vulnerability Database (NIST). Authoritative CVE metadata and CVSS scores.
Ransomware
The vulnerability is linked to known ransomware activity.
Reference: Microsoft CVE and vulnerability management, the full CVE-to-patch lookup ranked by real-world risk, and the Microsoft patching guide, how Intune, Windows Autopatch, Defender, and Azure Update Manager fit together.
Data notice: this page, the feeds, and the API are provided as is, for informational purposes only, without warranty of any kind. Senserva, LLC does not guarantee the accuracy, completeness, or timeliness of third-party data (MSRC, NVD, CISA KEV, EPSS) and accepts no liability for actions taken based on it; verify against the authoritative vendor advisory before acting. Built daily with Senserva Trustworthy AI. All use of this data is subject to the Senserva EULA.