Patch tracker / CVE reference / CVE-2026-40407

CVE-2026-40407

Updated July 21, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.

Patch this cycle
Not confirmed exploited yet, but the 30-day exploit probability is high (EPSS 72%).
Fixed by KB5087420 and 14 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 15 Microsoft security updates.

All about CVE-2026-40407: the Senserva AI read, whether it is exploited, the official patches, its change history, and the questions admins ask.

Senserva AI read on CVE-2026-40407Official patches for CVE-2026-40407Change historyAdmin questions

CVE-2026-40407 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 72%. Microsoft has shipped the fix: deploy one of the 15 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
72%
Severity
Critical
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Senserva AI Opinion for CVE-2026-40407

CLFS driver flaws like this one turn any low privilege foothold into SYSTEM, and the 9.8 CVSS score with a 72 percent EPSS exploit probability is unusually high for an elevation of privilege bug. Your exposure is Windows Server 2019 and 2022, including Server Core installations that often run infrastructure roles like domain controllers and hypervisors. CLFS has a long history of being weaponized quickly even before landing on CISA KEV, so treat the current 'not yet exploited' status as temporary.

Do this: Apply the Microsoft patch for this CVE to all Windows Server 2019 and 2022 systems, prioritizing domain controllers and Server Core hosts.

AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for CVE-2026-40407

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

Full tracking and change history for CVE-2026-40407

Published
2026-05-12
Last revised
2026-05-12
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 72%. CVSS 9.8 (Critical).

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

Official patch(es) for CVE-2026-40407

High priority: EPSS puts the odds of near-term exploitation high. In Intune or Defender, confirm whether the fixing updates KB5087420, KB5087423, KB5087424, KB5087470, KB5087471, KB5087537, KB5087538, KB5087539, KB5087541, KB5087544, KB5087545, KB5089466, KB5089549, KB5093998, KB5094127 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-2026-40407. 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.

KB5087420KB5087423KB5087424KB5087470KB5087471KB5087537KB5087538KB5087539KB5087541KB5087544KB5087545KB5089466KB5089549KB5093998KB5094127

Affected products

Common questions about CVE-2026-40407

Is CVE-2026-40407 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 72%.

What patch fixes CVE-2026-40407?

Microsoft fixed CVE-2026-40407 in KB5087420, KB5087423, KB5087424, KB5087470, KB5087471, KB5087537, KB5087538, KB5087539, KB5087541, KB5087544, KB5087545, KB5089466, KB5089549, KB5093998, KB5094127. Download from the Microsoft Update Catalog, or let Intune, Windows Update, or WSUS deliver it.

Which products are affected by CVE-2026-40407?

Windows 10 Version 1809 for 32-bit Systems, Windows 10 Version 1809 for x64-based Systems, Windows 11 Version 25H2 for ARM64-based Systems, Windows 11 Version 25H2 for x64-based Systems, Windows Server 2019, Windows Server 2025 (Server Core installation).

Can I ask my own AI about CVE-2026-40407?

Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2026-40407'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-2026-40407, the same updates also fix these:

CVE-2025-10263CVE-2025-54518CVE-2026-21530CVE-2026-32161CVE-2026-32170CVE-2026-32209CVE-2026-33828CVE-2026-33834

Authoritative references

Official CVE record (cve.org)NVD detailMicrosoft MSRCFIRST.org EPSS

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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.