CVE-2026-21509

EUVD-2026-4666
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
microsoftCNA
7.8 HIGH
LOCAL
LOW
NONE
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Base Score
CVSS 3.x
EPSS Score
Percentile: 99.4%
Affected Products (NVD)
VendorProductVersion
microsoft365_apps
-
microsoft365_apps
𝑥
< 2601
microsoftoffice
𝑥
< 2601
𝑥
= Vulnerable software versions
Early Detection
Affected products identified ahead of NVD analysis through intelligence sources (CNA/ADP records, vendor advisories, Enginsight analysis).
VendorProductVersionSource
microsoftoffice_2016
16.0.0 ≤
𝑥
< 16.0.5539.1001
CNA
microsoftoffice_2019
19.0.0 ≤
𝑥
< 16.0.10417.20095
CNA
Common Weakness Enumeration
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