CVE-2026-21509

UNKNOWNKnown Exploited

CISA Known Exploited Vulnerability

Please adhere to Microsoft’s recommended guidelines to address this vulnerability. Implement all final mitigations provided by the vendor for Office 2021, and apply the interim corresponding mitigations for Office 2016 and Office 2019 until the final patch becomes available. For more information please see: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509 ; https://nvd.nist.gov/vuln/detail/CVE-2026-21509

Remediation deadline: February 16, 2026

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.

Timeline

Published:January 26th, 2026 12:00 AM

Last modified:January 26th, 2026 12:00 AM

Added to KEV:January 26th, 2026

CVSS Scoring

No CVSS v3 score available

Affected Software

From NVD CPE configuration data

Vendors

Microsoft

Products

Office

Weaknesses (CWE)

CWE-807

References & Reports

Advisories, patches, and third-party reports

No references available.

Source: CISA KEV + NVD · Data may lag official sources by up to one minute