CVE-2026-21509

KEVMicrosoft Office Security Feature Bypass Vulnerability

Description

Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office could allow an unauthorized attacker to bypass a security feature locally. Some of the impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.

Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

CVSS 3.1 vectorCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

PublishedJan 26, 2026

Last modifiedJun 25, 2026

Added to KEVJan 26, 2026

Remediation dueFeb 16, 2026

References

msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509Vendor Advisory
vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerabilityThird Party Advisory
vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-office-security-feature-bypass-vulnerabilityMitigationThird Party Advisory
cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509US Government Resource

0 recent articles mention this CVE

Risk assessment · High

Actively exploited. Patch immediately.

Exploitation: Confirmed in the wild (CISA KEV)
Federal remediation deadline: Overdue by 253 days
CVSS: 7.8 HIGH
EPSS (30-day exploit probability): 70.8% · top 1% of all CVEs
Weakness: CWE-807

Recommended actions

1.Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
2.Treat as emergency change: patch or isolate internet-facing instances first.
3.Hunt for compromise: review logs for the disclosure window, not just from the patch date.

Assessment is derived automatically from the live signals above; verify against your own asset inventory.