CVE-2026-21513
Published 2026-02-10 · Updated 2026-06-17 · Source secure@microsoft.com
Summary
CVE-2026-21513 is a high-severity (CVSS 8.8) vulnerability in Microsoft Windows. CISA added it to the Known Exploited Vulnerabilities catalog on February 10, 2026, which means exploitation in the wild has been confirmed; US federal agencies had to remediate it by March 3, 2026. CISA does not currently list it as used in ransomware campaigns. Microsoft has 390 vulnerabilities in the KEV catalog, 117 of them linked to ransomware.
All 390 known-exploited Microsoft vulnerabilities →Description
Protection mechanism failure in MSHTML Framework allows an unauthorized attacker to bypass a security feature over a network.
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CISA Known-Exploited Vulnerability
Product: Microsoft — Windows
Name: Microsoft MSHTML Framework Protection Mechanism Failure Vulnerability
Date added: 2026-02-10 · Due: 2026-03-03
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.
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21513
- https://www.vicarius.io/vsociety/posts/cve-2026-21513-detection-script-security-feature-bypass-vulnerability-in-mshtml-framework
- https://www.vicarius.io/vsociety/posts/cve-2026-21513-mitigation-script-security-feature-bypass-vulnerability-in-mshtml-framework
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21513