Microsoft MSHTML Framework Protection Mechanism Failure Vulnerability

HIGH 8.8EXPLOITED (CISA KEV)CVE-2026-21513 · Published 10/02/2026 · updated 17/06/2026

Microsoft MSHTML Framework Protection Mechanism Failure Vulnerability. Actively exploited: CISA added this vulnerability to its Known Exploited Vulnerabilities catalog on 10/02/2026. Patch affected systems as an emergency.

Package	Affected versions	Patched versions
Windows Microsoft	Versions not published yet (product named by CISA KEV)

Description

Protection mechanism failure in MSHTML Framework allows an unauthorized attacker to bypass a security feature over a network.

References

msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21513 · Vendor Advisory
vicarius.io/vsociety/posts/cve-2026-21513-detection-script-security-feature-bypass-vulnerability-in-mshtml-framework · Third Party Advisory
vicarius.io/vsociety/posts/cve-2026-21513-mitigation-script-security-feature-bypass-vulnerability-in-mshtml-framework · Mitigation
cisa.gov/known-exploited-vulnerabilities-catalog · US Government Resource
CISA KEV · CVE-2026-21513

Running one of these products? Scan your site to see whether it exposes a vulnerable version.

Scan my site free