CVE-2026-21509
HIGH CISA KEV EPSS 99.4%
Published Jan 26, 20265mo ago · Modified Jun 17, 20262w ago
7.8 CVSS 3.1
Published Jan 26, 2026 5mo ago
Last Modified Jun 17, 2026 2w ago
KEV Listed Jan 26, 2026 5mo ago
KEV Due Feb 16, 2026 136d overdue
Description
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
CVSS Details
Base Score
Exploitability
Impact
Vector string
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Attack Vector Local
Attack Complexity Low
Privileges Required None
User Interaction Required
Scope Unchanged
Confidentiality High
Integrity High
Availability High
Threat Intelligence
CISA Known Exploited Overdue 136d
- Added
- Jan 26, 2026
- Due
- Feb 16, 2026
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
EPSS Exploit Probability
99.4% percentile
Exploit & Patch Status
Actively Exploited (KEV)
No Patch Available
Weaknesses 1
CWE-807
Affected Products 10
| Vendor | Product | Version | Range |
|---|---|---|---|
| microsoft | 365_apps | * | any |
| microsoft | 365_apps | * | any |
| microsoft | office | 2016 | any |
| microsoft | office | 2016 | any |
| microsoft | office | 2019 | any |
| microsoft | office | 2019 | any |
| microsoft | office_long_term_servicing_channel | 2021 | any |
| microsoft | office_long_term_servicing_channel | 2021 | any |
| microsoft | office_long_term_servicing_channel | 2024 | any |
| microsoft | office_long_term_servicing_channel | 2024 | any |
References 4
- msrc.microsoft.com https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509
- cisa.gov https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509
- vicarius.io https://www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerability
- vicarius.io https://www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-office-security-feature-bypass-vulnerability
Remediation
No remediation data recorded yet
Check vendor advisories and the NVD entry for patch availability.