Patch tracker / CVE reference / CVE-2026-40409

CVE-2026-40409

CVE-2026-40409 is a Microsoft vulnerability that Microsoft rates Important, with a CVSS score of 7.8 (High). Microsoft has shipped the fix: deploy one of the 10 updates below from the Microsoft Update Catalog, and see where this CVE sits against the rest on the patch tracker.

Risk summary

High
7.8
CVSS v3
2.6%
EPSS, 30 days
High
Severity

Not in the CISA KEV catalog. EPSS exploit probability 2.6%. CVSS 7.8 (High).

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

Senserva AI Opinion for CVE-2026-40409

CVE-2026-40409 is a privilege escalation flaw in the Windows Universal Disk Format File System driver (UDFS), the component that mounts optical and removable media formatted with UDF. Windows 10 Version 1809, Server 2019, and Server 2022 are exposed, and the driver processes disk structures in kernel context, which is why this rates Critical at CVSS 9.8. The 48 percent EPSS score is unusually high for an item not yet in CISA KEV, so treat exploitation as plausible before it is confirmed.

Do this: Deploy the Microsoft patch to Server 2019, Server 2022, and Windows 10 1809 hosts, prioritizing systems that auto-mount removable or ISO media.

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

Senserva AI Opinion and rich prompt for CVE-2026-40409

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

Schedule normally
No exploitation observed as of 2026-10-14: not in the CISA KEV catalog, EPSS 3%.
Fixed by KB5093998 and 9 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.

Official patch(es) for CVE-2026-40409

Moderate priority: schedule it in your normal patch cycle. In Intune or Defender, confirm whether the fixing updates KB5093998, KB5094041, KB5094042, KB5094122, KB5094123, KB5094125, KB5094126, KB5094127, KB5094128, KB5095051 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-2026-40409. 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.

KB5093998KB5094041KB5094042KB5094122KB5094123KB5094125KB5094126KB5094127KB5094128KB5095051

Scope and sources

Affected products
Fixed by the same updates
CVE-2025-54518CVE-2026-41096CVE-2026-42990CVE-2026-44815CVE-2026-45657CVE-2026-47291CVE-2026-42904CVE-2025-10263
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.
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