Vulnerability Description
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
CVSS Score
7.8
HIGH
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Microsoft | 365 Apps | - |
| Microsoft | Office | 2016 |
| Microsoft | Office Long Term Servicing Channel | 2021 |
Related Weaknesses (CWE)
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509Vendor Advisory
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoftThird Party Advisory
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsofMitigationThird Party Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-US Government Resource
FAQ
What is CVE-2026-21509?
CVE-2026-21509 is a vulnerability with a CVSS score of 7.8 (HIGH). Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
How severe is CVE-2026-21509?
CVE-2026-21509 has been rated HIGH with a CVSS base score of 7.8/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-21509?
Check the references section above for vendor advisories and patch information. Affected products include: Microsoft 365 Apps, Microsoft Office, Microsoft Office Long Term Servicing Channel.