CISA Known Exploited Vulnerability
This vulnerability is actively exploited in the wild and listed in the CISA Known Exploited Vulnerabilities catalog.
Remediation Deadline: Feb 16, 2026
CVE-2026-21509
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.
Required Action
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
Vulnerability Overview
- Severity
- High
- CISA KEV
- Yes
- Ransomware
- Unknown
- Published
- Jan 26, 2026
- KEV Added
- Jan 26, 2026
- Due Date
- Feb 16, 2026
- Related Articles
- 0
Vendor
Microsoft
Office