Patch tracker / CVE reference / CVE-2026-40402

CVE-2026-40402

CVE-2026-40402 is a Microsoft vulnerability that Microsoft rates Critical, with a CVSS score of 9.3 (Critical). Microsoft has shipped the fix: deploy one of the 4 updates below from the Microsoft Update Catalog, and see where this CVE sits against the rest on the patch tracker.

Risk summary

Critical
9.3
CVSS v3
2.3%
EPSS, 30 days
Critical
Severity

Not in the CISA KEV catalog. EPSS exploit probability 2.3%. CVSS 9.3 (Critical).

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

Senserva AI Opinion for CVE-2026-40402

This is a Hyper-V elevation of privilege flaw rated Critical with a CVSS score of 9.8, unusually high for an EoP bug, which suggests a low bar to abuse from within a guest or host context. Exposure is narrow but specific: Windows Server 2022 including Server Core, plus Windows 11 Version 23H2 for ARM64 systems. It is not in CISA KEV and has no confirmed ransomware use, but the 80 percent EPSS score signals that working exploit code is likely near term.

Do this: Prioritize patching your Hyper-V hosts running Windows Server 2022 and the affected ARM64 Windows 11 23H2 systems in this cycle rather than waiting for the next scheduled window.

AI-generated from public data, 2026-07-26. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for CVE-2026-40402

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 2%.
Fixed by KB5087420 and 3 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-2026-40402

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 KB5087420, KB5087424, KB5087545, KB5093998 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-2026-40402. 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.

KB5087420KB5087424KB5087545KB5093998

Scope and sources

Affected products
Fixed by the same updates
CVE-2025-54518CVE-2026-41089CVE-2026-41096CVE-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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