Vulnerability details
CVE-2026-21509
Actively exploited
Microsoft 365 Apps for EnterpriseMicrosoft OfficeMicrosoft Office LTSC
Microsoft Office Security Feature Bypass Vulnerability
CVSS 3.1
7.8High
Official description
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
CVSS scores
| Score | Version | Source | Vector |
|---|---|---|---|
| 7.8High | 3.1 | CVEProject cvelistV5 (CNA) (microsoft) | 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 |
Affected products
| Vendor | Product | Versions | Source |
|---|---|---|---|
| Microsoft | Microsoft 365 Apps for Enterprise | 16.0.1 ≤ v < https://aka.ms/OfficeSecurityReleases | CVEProject cvelistV5 (CNA) |
| Microsoft | Microsoft Office 2016 | 16.0.0 ≤ v < 16.0.5539.1001 | CVEProject cvelistV5 (CNA) |
| Microsoft | Microsoft Office 2019 | 19.0.0 ≤ v < 16.0.10417.20095 | CVEProject cvelistV5 (CNA) |
| Microsoft | Microsoft Office LTSC 2021 | 16.0.1 ≤ v < https://aka.ms/OfficeSecurityReleases | CVEProject cvelistV5 (CNA) |
| Microsoft | Microsoft Office LTSC 2024 | 16.0.0 ≤ v < https://aka.ms/OfficeSecurityReleases | CVEProject cvelistV5 (CNA) |
References and advisories
4- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509 vendor-advisorypatch
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509 government-resource
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerability
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-office-security-feature-bypass-vulnerability
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Details
- Published
- 2026-01-26
- Last updated
- 2026-07-31
- State
- Published
- Assigner (CNA)
- microsoft
- Kolun priority
- 87 · Critical
CISA KEV catalog
- Date added
- 2026-01-26
- Due date
- 2026-02-16
- Used in ransomware
- Unknown
Exploit prediction (EPSS)
70.82%
Probability of exploitation in 30 days
99.4%
Percentile (among all CVEs)
SSVC assessment (CISA)
- Automatable
- No
- Exploitation
- Active
- Technical impact
- Total
Weaknesses (CWE)
- CWE-807Reliance on Untrusted Inputs in a Security Decision