CVE-2026-21509
Published 2026-01-26 · Updated 2026-06-25 · Source secure@microsoft.com
Summary
CVE-2026-21509 is a high-severity (CVSS 7.8) vulnerability in Microsoft Office. CISA added it to the Known Exploited Vulnerabilities catalog on January 26, 2026, which means exploitation in the wild has been confirmed; US federal agencies had to remediate it by February 16, 2026. CISA does not currently list it as used in ransomware campaigns. Microsoft has 390 vulnerabilities in the KEV catalog, 117 of them linked to ransomware.
All 390 known-exploited Microsoft vulnerabilities →Description
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CISA Known-Exploited Vulnerability
Product: Microsoft — Office
Name: Microsoft Office Security Feature Bypass Vulnerability
Date added: 2026-01-26 · Due: 2026-02-16
Required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerability
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-office-security-feature-bypass-vulnerability
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509