Actively exploited
Listed in CISA’s Known Exploited Vulnerabilities catalog since January 26, 2026.
CVE-2026-21509
Microsoft Office Security Feature Bypass Vulnerability
Added to KEV January 26, 2026
Alert details
- Source feed
- CISA KEV
- CVE ID
- CVE-2026-21509
- CWE
- CWE-807
- Affected products
- Office · Microsoft Office · Microsoft
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.
What it means for your business
Microsoft Office is listed in CISA's Known Exploited Vulnerabilities catalog (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. CISA remediation due date: 2026-02-16. If you need help checking exposure, call (864) 335-9223.
Required action
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 due date: February 16, 2026
Sources
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