CVE-2026-21509
Actively exploited. CVE-2026-21509 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2026-01-26) — exploitation has been observed in the wild, and US federal agencies are required to remediate it under BOD 22-01. Treat patching as urgent.
Public exploit code is available. Proof-of-concept or working exploit code for CVE-2026-21509 is indexed in GitHub PoC. Expect opportunistic scanning and exploitation attempts — prioritize remediation.
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.
CSIRTS triage
- What
- A security feature bypass vulnerability could allow unauthorized attackers to bypass security features locally.
- Who is affected
- Users of Microsoft Office are affected, especially those on end-of-life versions.
- Urgency
- Remediation is critical due to active exploitation and the potential for unauthorized access.
- Action
- Transition to a supported version of Microsoft Office.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Exploitation confirmedAlready exploited in the wild (CISA KEV) — the prediction phase is over. Patch now. Riskier than 99% of all EPSS-scored CVEs.
Exploit availability
Public exploit or proof-of-concept code for CVE-2026-21509 is indexed in these free datasets. Available exploit code raises real-world risk independent of the CVSS score.
- GitHub PoCPublic proof-of-concept repositories on GitHub reference this CVE.look it up ↗
Advisory coverage (1)
- criticalexploitedCVE-2026-21509: Microsoft Office Security Feature Bypass Vulnerabilitycisa-kev · 2026-01-26
External references
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[](https://www.csirts.com/cve/CVE-2026-21509)