Patch tracker / CVE reference / CVE-2026-40409

CVE-2026-40409

CVE-2026-40409 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 54%. 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

Critical

9.8

CVSS

54%

EPSS, 30 days

Critical

Severity

Not in the CISA KEV catalog. EPSS exploit probability 54%. CVSS 9.8 (Critical).

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.

I am an IT admin assessing a vulnerability. Facts for CVE-2026-40409 (source: https://senserva.com/cve/CVE-2026-40409.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- CVE-2026-40409: Critical severity Microsoft vulnerability, CVSS 9.8
- EPSS 30-day exploitation probability: 54%
- Actively exploited (CISA KEV): no
- Fixed by: KB5093998, KB5094041, KB5094042, KB5094122, KB5094123, KB5094125, KB5094126, KB5094127, KB5094128, KB5095051
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 54%).

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

Official patch(es) for CVE-2026-40409

High priority: EPSS puts the odds of near-term exploitation high. 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.

KB5093998 KB5094041 KB5094042 KB5094122 KB5094123 KB5094125 KB5094126 KB5094127 KB5094128 KB5095051

Scope and sources

Affected products

Fixed by the same updates

CVE-2026-40378 CVE-2026-42982 CVE-2026-42990 CVE-2026-44800 CVE-2026-48564 CVE-2026-48571 CVE-2026-48572 CVE-2024-43582

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.