CVE-2026-21513

CISA KEV

Published February 10, 2026 · Updated April 3, 2026

high

What This Means

**CVE-2026-21513: MSHTML Protection Mechanism Bypass** The MSHTML rendering engine in Microsoft Windows fails to properly enforce a security protection mechanism, allowing an attacker to bypass this control via network-based exploitation. This enables unauthorized code execution or information disclosure depending on the specific protection mechanism affected and attack vector. Apply the latest Windows security updates from Microsoft immediately, and prioritize systems where users access untrusted content (email, web browsing) or host web applications.

Official Description+

Microsoft MSHTML Framework contains a protection mechanism failure vulnerability that could allow an unauthorized attacker to bypass a security feature over a network.

Affected Products

Vendor	Product
Microsoft	Windows

Patch Status

Patch by 2026-03-03

Recommended Actions

Check if your systems use any of the affected products listed above.
Apply vendor patches immediately if available.
This vulnerability is in CISA's Known Exploited Vulnerabilities catalog — prioritize remediation.
Monitor vendor advisories for updates and additional mitigations.
Review logs for indicators of compromise related to CVE-2026-21513.

Related Coverage

Vvulnerability

CVE-2026-21513: Microsoft MSHTML Security Bypass Enables Network-Based Exploitation on Windows

CVE-2026-21513 is a protection mechanism failure in Microsoft's MSHTML rendering engine that allows an unauthenticated remote attacker to bypass a security control via network-based delivery of malicious HTML content. Successful exploitation can lead to unauthorized code execution or information disclosure, and CISA has mandated federal agency patching by March 3, 2026. Organizations should apply current Windows cumulative updates immediately and prioritize systems where users process email or run applications embedding MSHTML.

CISA KEV·52d ago·3 min read