# CVE-2026-21509: Microsoft Office Security Feature Bypass Vulnerability

> CVE-2026-21509: Microsoft Office Security Feature Bypass Vulnerability. CVSS 7.8 (CVSS 3.1), in CISA KEV.

Canonical: https://rewindex.com/cve/CVE-2026-21509
Last updated: 2026-07-30T20:47:35Z

- Published: 2026-01-26 17:06 UTC · Updated: 2026-07-30 20:47 UTC · Assigner: microsoft
- CVSS: 7.8 (CVSS 3.1) · Severity: High · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C
- EPSS: 70.8%, 99th percentile (scored 2026-10-25)
- CISA KEV: yes, added 2026-01-26, federal due date 2026-02-16, ransomware use: Unknown
- CWE: CWE-807

## Description

Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

## CISA 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.

## Affected vendors and products

- Microsoft: Microsoft 365 Apps for Enterprise
- Microsoft: Microsoft Office 2016
- Microsoft: Microsoft Office 2019
- Microsoft: Microsoft Office LTSC 2021
- Microsoft: Microsoft Office LTSC 2024

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-21509)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-21509)
- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-21509 · Markdown: https://rewindex.com/cve/CVE-2026-21509.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-21509 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:13:22.492Z