Coverage › CVE-2026-21509
CVE-2026-21509 Unmapped
Microsoft Office Security Feature Bypass Vulnerability
- Vendor / product
- Microsoft — Office
- Description (CISA)
- 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.
- Added to KEV
- 2026-01-26 — after the latest CTID mapping snapshot (2025-07-28)
- Due date
- 2026-02-16
- 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.
- Known ransomware use
- Unknown
- CWE
- CWE-807
- CISA notes
- 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 - Elsewhere
- cve.org · NVD · CISA KEV · JSON
ATT&CK techniques
No public source states how this vulnerability is exploited in ATT&CK terms.
The only authoritative CVE → ATT&CK mapping in the open — CTID's Mappings Explorer, pinned to a KEV snapshot of 2025-07-28 and ATT&CK 16.1 — does not include CVE-2026-21509. This entry was added to KEV on 2026-01-26, after that snapshot; of the 283 entries added since, 0 have a mapping. CISA's catalogue carries no technique field. kevmap does not infer techniques from the CWE (CWE-807) — here is why — and does not guess.
This page will change state automatically if a mapping is published. What is shown above is everything CISA publishes about the entry.