MSRXVulnerabilities / CVE-2026-21509
CVE-2026-21509
Published 2026-01-26 · Analyzed
CVE-2026-21509
Microsoft Office Security Feature Bypass Vulnerability
Exploited in the wild: CISA added it to the Known Exploited Vulnerabilities catalog on 2026-01-26, with a fix-by date of 2026-02-16. Patch it first.
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
7.8 HIGH
CVSS 3.1 · CNA · microsoft.com
CVSS 3.1 · CNA · microsoft.com
71%
chance of exploitation in the next 30 days (EPSS; in the top 1% of all CVEs)
chance of exploitation in the next 30 days (EPSS; in the top 1% of all CVEs)
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
Scores
Affected products
- microsoft 365 apps: all versions
- microsoft office: 2016; 2019
- microsoft office long term servicing channel: 2021; 2024
Weakness: CWE-807
4 references (advisories, patches, write-ups)
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509 · Vendor Advisory
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerability · Third Party Advisory
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-office-security-feature-bypass-vulnerability · Mitigation, Third Party Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509 · US Government Resource
Sources: NVD, CVE.org, FIRST EPSS. Missing ones did not answer or have no record yet.