CVE entry · CVE-2026-21509
CVE-2026-21509: Microsoft Office Security Feature Bypass Vulnerability
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.
- Actively exploited: added to CISA’s KEV catalog on January 26, 2026.
- Use by ransomware: not established so far.
- Remediation deadline for US federal agencies: February 16, 2026.
Description from CISA’s KEV catalog.
What to do
- Check whether your estate includes Microsoft Office, including internet-facing devices.
- Apply the vendor’s patch or mitigations (references below). Failing that, isolate the product or stop using it, as CISA requires of US federal agencies.
- An exploited vulnerability has often been used before it was fixed: look for signs of compromise, especially on internet-facing devices.
References
Other Microsoft vulnerabilities
-
Microsoft Windows Command Injection Vulnerability
-
Microsoft SharePoint Code Injection Vulnerability
-
Microsoft Windows Heap-Based Buffer Overflow Vulnerability
-
Microsoft Windows Link Following Vulnerability
-
Microsoft SQL Server Remote Code Execution Vulnerability
-
Microsoft SharePoint Weak Authentication Vulnerability