CVE DATABASE / CVE-2026-21509
CVE-2026-21509
Microsoft Office Security Feature Bypass Vulnerability
CVSS 7.8 · HIGH
⚠ CISA KEV — ACTIVELY EXPLOITED
On the CISA KEV catalog
Confirmed exploited in the wild. Added 2026-01-26.
Federal remediation 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.
Summary
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
CVSS 3.1 breakdown
| Base score | 7.8 (HIGH) |
| Vector | CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H |
| Attack vector | LOCAL |
| Attack complexity | LOW |
| Privileges required | NONE |
| User interaction | REQUIRED |
| Scope | UNCHANGED |
| Confidentiality | HIGH |
| Integrity | HIGH |
| Availability | HIGH |
Weakness type (CWE)
Affected products
Microsoft 365 appsMicrosoft officeMicrosoft office long term servicing channel
Check this CVE live
Use our free CVE Lookup tool for the latest NVD record, or browse the full CISA KEV catalog.
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
Data: NIST NVD + CISA KEV. NVD last modified 2026-02-11. Always verify against the vendor advisory before acting.