VulnerabilityAnalyzed
CVE-2026-21513
Microsoft MSHTML Framework Protection Mechanism Failure Vulnerability
KEVHIGH 8.8EPSS 15.6%
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 3 March 2026). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
Description
Protection mechanism failure in MSHTML Framework allows an unauthorized attacker to bypass a security feature over a network.
- CVSS 3.1
- 8.8 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- EPSS
- 15.64% probability · 97th percentile
- CISA KEV
- Listed 10 February 2026 · due 3 March 2026
- Weakness
- CWE-693
- Affected
- microsoft/windows 10 1607 · microsoft/windows 10 1809 · microsoft/windows 10 21h2 · microsoft/windows 10 22h2 · microsoft/windows 11 23h2 · microsoft/windows 11 24h2 · microsoft/windows 11 25h2 · microsoft/windows server 2012 · microsoft/windows server 2016 · microsoft/windows server 2019 · microsoft/windows server 2022 · microsoft/windows server 2022 23h2 · microsoft/windows server 2025
- Source
- secure@microsoft.com
CISA notes
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. https://msrc.microsoft.com/update-guide/advisory/CVE-2026-21513 ; https://nvd.nist.gov/vuln/detail/CVE-2026-21513
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21513Vendor Advisory
- https://www.vicarius.io/vsociety/posts/cve-2026-21513-detection-script-security-feature-bypass-vulnerability-in-mshtml-frameworkThird Party Advisory
- https://www.vicarius.io/vsociety/posts/cve-2026-21513-mitigation-script-security-feature-bypass-vulnerability-in-mshtml-frameworkMitigation, Third Party Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21513US Government Resource
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.