Patch tracker / CVE reference / CVE-2026-21509

CVE-2026-21509

High severity Microsoft vulnerability, CVSS 7.8. Fixed by 1 Microsoft security update.

HighCISA KEV

Risk summary

CVSS base
7.8
EPSS exploit probability
72%
Severity
High

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.

What to do

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.

Official patch for CVE-2026-21509

Apply the Microsoft security update below to fix CVE-2026-21509. Each KB page links to the Microsoft Update Catalog download for every affected product.

KB5002713

Affected products

  • Microsoft 365 Apps for Enterprise for 32-bit Systems
  • Microsoft Office 2019 for 32-bit editions
  • Microsoft Office 2019 for 64-bit editions

Authoritative references

NVD detailMicrosoft MSRCCISA KEV catalogFIRST.org EPSS

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

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Lexicon: the terms on this page
CVE
Common Vulnerabilities and Exposures. A unique ID for one publicly known vulnerability, such as CVE-2025-1234.
KB
Microsoft Knowledge Base article. The identifier for a specific Microsoft update.
KEV
CISA Known Exploited Vulnerabilities. CVEs confirmed exploited in the wild. Fix these first.
CVSS
Common Vulnerability Scoring System. A standardized Severity score from 0 to 10.
EPSS
Exploit Prediction Scoring System. The probability a CVE will be exploited in the next 30 days.
MSRC
Microsoft Security Response Center. Microsoft's Patch Tuesday advisories and KB-to-CVE mapping.
NVD
National Vulnerability Database (NIST). Authoritative CVE metadata and CVSS scores.
Ransomware
The vulnerability is linked to known ransomware activity.