CVE-2026-21509
Microsoft Office Security Feature Bypass Vulnerability
Microsoft Office Security Feature Bypass Vulnerability is confirmed as actively exploited and is listed in the CISA KEV catalog.
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 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
Description
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
Severity
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:CExploitation Context
as of October 14, 2026- CISA added CVE-2026-21509 to the KEV catalog on the day its CVE record was published. The median for entries added in 2026 so far is 15 days.
- It is one of 391 Microsoft entries in the CISA KEV catalog, and one of 40 added in 2026.
- Its current EPSS score (70.8%) is higher than that of 58% of CISA KEV entries.
Affected Products
| Vendor | Product | Affected versions |
|---|---|---|
| Microsoft | Microsoft Microsoft 365 Apps for Enterprise | 16.0.1 to <https://aka.ms/OfficeSecurityReleases |
| Microsoft | Microsoft Microsoft Office 2016 | 16.0.0 to <16.0.5539.1001 |
| Microsoft | Microsoft Microsoft Office 2019 | 19.0.0 to <16.0.10417.20095 |
| Microsoft | Microsoft Microsoft Office LTSC 2021 | 16.0.1 to <https://aka.ms/OfficeSecurityReleases |
| Microsoft | Microsoft Microsoft Office LTSC 2024 | 16.0.0 to <https://aka.ms/OfficeSecurityReleases |
References
3 LinksRecord Details
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Related
Tool categories
CVE record data © The MITRE Corporation, used under the CVE Terms of Use. Exploited-in-the-wild data from the CISA Known Exploited Vulnerabilities catalog (CC0). Exploit prediction scores by FIRST EPSS (first.org/epss). This site is not endorsed or certified by MITRE, NVD, CISA, or FIRST.