CVE-2026-21509

Microsoft Office Security Feature Bypass Vulnerability

CVE-2026-21509 is fixed in 2 products on 1 platform, first by KB5002713, released January 26, 2026. It is being exploited: CISA added it to the Known Exploited Vulnerabilities catalog on January 26, 2026. Patch Radar priority: Patch now.

Patch nowCISA KEV

CVSS

7.8

Important

Exploitation

Exploited

Reported by the vendor

CISA KEV

Jan 26, 2026

Federal due date Feb 16, 2026

EPSS

0.7080

99th percentile

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

Where it's fixed

Product	Fix	Released
Microsoft
Microsoft Office 2016 (32-bit edition)	KB5002713	Jan 26, 2026
Microsoft Office 2016 (64-bit edition)	KB5002713	Jan 26, 2026

Details

Published
January 26, 2026
Weakness
Reliance on Untrusted Inputs in a Security Decision
CISA 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.
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509

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