Jan 2026: Microsoft Office Security Feature Bypass Vulnerability
CVE-2026-21509 Published on January 26, 2026
Microsoft Office Security Feature Bypass Vulnerability
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
Known Exploited Vulnerability
This Microsoft Office Security Feature Bypass Vulnerability is part of CISA's list of Known Exploited Vulnerabilities. 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.
The following remediation steps are recommended / required by February 16, 2026: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Weakness Type
Reliance on Untrusted Inputs in a Security Decision
The application uses a protection mechanism that relies on the existence or values of an input, but the input can be modified by an untrusted actor in a way that bypasses the protection mechanism.
Products Associated with CVE-2026-21509
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Affected Versions
Microsoft 365 Apps for Enterprise:- Version 16.0.1 and below https://aka.ms/OfficeSecurityReleases is affected.
- Version 16.0.0 and below 16.0.5539.1001 is affected.
- Version 19.0.0 and below 16.0.10417.20095 is affected.
- Version 16.0.1 and below https://aka.ms/OfficeSecurityReleases is affected.
- Version 16.0.0 and below https://aka.ms/OfficeSecurityReleases is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.