Patch tracker / CVE reference / CVE-2026-33840

CVE-2026-33840

CVE-2026-33840 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 5 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
2.2%
EPSS, 30 days
High
Severity

Not in the CISA KEV catalog. EPSS exploit probability 2.2%. CVSS 7.8 (High).

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

Senserva AI Opinion for CVE-2026-33840

Win32k reaches the newest platforms here: Windows Server 2025 Server Core and Windows 11 Version 25H2 carry this Critical (CVSS 9.8) escalation with a 72 percent EPSS exploit probability. The win32k subsystem's exploitation history is long enough that a high EPSS score on a fresh variant deserves belief, even on brand-new builds. This closes the loop with the 1809-era win32k flaws in the same cycle: no branch is exempt.

Do this: Include Windows 11 25H2 and Server 2025 in the win32k patching push and verify with a vulnerability scan across all branches.

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

Senserva AI Opinion and rich prompt for CVE-2026-33840

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 KB5087423 and 4 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-2026-33840

Moderate priority: schedule it in your normal patch cycle. In Intune or Defender, confirm whether the fixing updates KB5087423, KB5087539, KB5089466, KB5089548, KB5089549 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-2026-33840. 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.

KB5087423KB5087539KB5089466KB5089548KB5089549

Scope and sources

Affected products
Fixed by the same updates
CVE-2025-54518CVE-2026-41089CVE-2026-41096CVE-2026-34329CVE-2026-40403CVE-2026-40415CVE-2026-34332CVE-2026-33834
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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