Patch tracker / CVE reference / CVE-2026-21509

CVE-2026-21509

CVE-2026-21509 is a high severity Microsoft vulnerability with a CVSS score of 7.8. It is in the CISA Known Exploited Vulnerabilities catalog: attackers are using it in the wild, which makes it a fix-first item. Microsoft has shipped the fix: deploy the update below from the Microsoft Update Catalog, and see where this CVE sits against the rest on the patch tracker.

Risk summary

HighCISA KEV

7.8

CVSS

72%

EPSS, 30 days

High

Severity

Yes

Exploited in the wild

Listed in the CISA Known Exploited Vulnerabilities catalog, confirmed exploited in the wild. EPSS exploit probability 72%. CVSS 7.8 (High).

This CVE is among the top 25% of tracked Microsoft CVEs by EPSS exploit probability, and one of 3 actively-exploited CVEs in January 2026.

Senserva AI Opinion for CVE-2026-21509

CVE-2026-21509 is a security feature bypass in Microsoft Office 2019 and Microsoft 365 Apps for Enterprise, meaning it defeats a protection Office relies on rather than granting direct code execution on its own. What sets it apart is that CISA confirmed active exploitation on 2026-01-26 and EPSS puts exploit probability at 72 percent, so attackers are already using it to weaken Office defenses that likely feed into a broader phishing or document based attack chain. Any workstation running these Office builds is exposed.

Do this: Deploy the current Microsoft Office security update to all Office 2019 and Microsoft 365 Apps for Enterprise endpoints now, prioritizing internet exposed and email heavy users.

AI-generated from public data, 2026-07-23. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for CVE-2026-21509

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-2026-21509 (source: https://senserva.com/cve/CVE-2026-21509.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- CVE-2026-21509: High severity Microsoft vulnerability, CVSS 7.8
- EPSS 30-day exploitation probability: 72%
- Actively exploited (CISA KEV): YES
- Fixed by: KB5002713
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 now

Exploited in the wild: confirmed by the CISA KEV catalog, not predicted.

Fixed by KB5002713. Download from the Microsoft Update Catalog, or deploy via Windows Update, Intune, or WSUS.

Do this now: Patch now and verify deployment on every exposed device.

Official patch(es) for CVE-2026-21509

Treat as urgent: it is being exploited in the wild (CISA KEV), so patch ahead of items that are not. In Intune or Defender, confirm whether the fixing update KB5002713 are installed across the affected products. Senserva does this automatically across your tenant and flags every missing patch.

Apply the Microsoft security update below to fix CVE-2026-21509. 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.

KB5002713

Scope and sources

Affected products

Authoritative references

Official CVE record (cve.org)NVD detail Microsoft MSRC CISA KEV catalog FIRST.org EPSS

Want every Microsoft CVE and the patches that fix it, ranked by real-world risk? See the Microsoft Patch Tracker.