Microsoft Office Security Feature Bypass
What to do
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
CISA deadline 2026-02-16 · passed 6 months ago · applies to US federal civilian agencies; used elsewhere as a reference SLA
What happened
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.
Who is affected
Microsoft Office. Affected version ranges are listed in the vendor advisory and the NVD entry linked under Sources.
Weakness class: CWE-807.
Timeline
- Added to CISA KEVExploitation in the wild confirmed by CISA
- CISA remediation deadlinepassed 6 months ago
Sources
- NVD entry for CVE-2026-21509 nvd.nist.gov/vuln/detail/CVE-2026-21509
- CISA Known Exploited Vulnerabilities catalog www.cisa.gov/known-exploited-vulnerabilities-catalog
- msrc.microsoft.com msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509
- nvd.nist.gov nvd.nist.gov/vuln/detail/CVE-2026-21509