CVE-2026-21509
Microsoft 365 Apps for Enterprise, Microsoft Office 2016, Microsoft Office 2019
Published 26 Jan 2026 · updated 25 Jun 2026 · Analyzed
7.8 High · CVSS 3.1, microsoft.com
Exploited in the wild
CISA added this to its Known Exploited Vulnerabilities catalog on 26 Jan 2026, with a remediation deadline of 16 Feb 2026 for US federal agencies.
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.
Description
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
References
- msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509 · Vendor Advisory
- www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerability · Third Party Advisory
- www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-office-security-feature-bypass-vulnerability · Mitigation, Third Party Advisory
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509 · US Government Resource