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.
High severity Microsoft vulnerability, CVSS 7.8. Fixed by 1 Microsoft security update.
Risk summary
Updated July 25, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.
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.
Full tracking and change history for CVE-2026-21509
Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.
Exploitation and severity
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.
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.
Affected products
Common questions about CVE-2026-21509
Is CVE-2026-21509 actively exploited?
Yes. CVE-2026-21509 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, which means exploitation in the wild has been confirmed. Its EPSS exploit probability is 72%.
What patch fixes CVE-2026-21509?
Microsoft fixed CVE-2026-21509 in KB5002713. Download from the Microsoft Update Catalog, or let Intune, Windows Update, or WSUS deliver it.
Which products are affected by CVE-2026-21509?
Microsoft 365 Apps for Enterprise for 32-bit Systems, Microsoft Office 2019 for 32-bit editions, Microsoft Office 2019 for 64-bit editions.
Can I ask my own AI about CVE-2026-21509?
Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2026-21509's key facts: severity, CVSS, EPSS exploit probability, CISA KEV status, and the fixing KB. Copy it into Claude, ChatGPT, or Copilot for a triage plan; the data is refreshed twice a day (5 AM and 3 PM US Central).
Authoritative references
Want every Microsoft CVE and the patches that fix it, ranked by real-world risk? See the Microsoft Patch Tracker.
