CVE-2026-21513: Microsoft MSHTML Framework Protection Mechanism Failure Vulnerability

What it is

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

Exploitation evidence

First exploit evidence seen: 2026-02-10 (earliest date across the sources below).

Exploited in the wild

• CISA KEV: listed since 2026-02-10. Source

Sources: CISA KEV.

How to fix it

CISA 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. (source: CISA KEV)

Fixed versions

• microsoft windows 10 1607: upgrade to 10.0.14393.8868 or later
• microsoft windows 10 1809: upgrade to 10.0.17763.8389 or later
• microsoft windows 10 21h2: upgrade to 10.0.19044.6937 or later
• microsoft windows 10 22h2: upgrade to 10.0.19045.6937 or later
• microsoft windows 11 23h2: upgrade to 10.0.22631.6649 or later
• microsoft windows 11 24h2: upgrade to 10.0.26100.7781 or later
• microsoft windows 11 25h2: upgrade to 10.0.26200.7781 or later
• microsoft windows server 2016: upgrade to 10.0.14393.8868 or later
• microsoft windows server 2019: upgrade to 10.0.17763.8389 or later
• microsoft windows server 2022: upgrade to 10.0.20348.4711 or later
• microsoft windows server 2022 23h2: upgrade to 10.0.25398.2149 or later
• microsoft windows server 2025: upgrade to 10.0.26100.32313 or later

Derived from the NVD CPE configuration (versionEndExcluding / versionEndIncluding). Always confirm with the vendor advisory.

Vendor advisories and patches

• https://msrc.microsoft.com/update-guide/advisory/CVE-2026-21513 (CISA KEV notes)
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21513 (Vendor Advisory)
• https://www.vicarius.io/vsociety/posts/cve-2026-21513-mitigation-script-security-feature-bypass-vulnerability-in-mshtml-framework (Mitigation, Third Party Advisory)

MITRE ATT&CK mitigations for this chain

• M1050 Exploit Protection (for T1211) : Security applications that look for behavior used during exploitation such as Windows Defender Exploit Guard (WDEG) and the Enhanced Mitigation Experience Toolkit (EMET) can be used to mitigate some exploitation behavior. Control flow integrity checking is another way to potentially identify and stop a software exploi
• M1051 Update Software (for T1211) : Update software regularly by employing patch management for internal enterprise endpoints and servers.
• M1019 Threat Intelligence Program (for T1211) : Develop a robust cyber threat intelligence capability to determine what types and levels of threat may use software exploits and 0-days against a particular organization.
• M1048 Application Isolation and Sandboxing (for T1211) : Make it difficult for adversaries to advance their operation through exploitation of undiscovered or unpatched vulnerabilities by using sandboxing. Other types of virtualization and application microsegmentation may also mitigate the impact of some types of exploitation. Risks of additional exploits and weaknesses in t

Detection Generic guidance

Response checklist Generic guidance

1. Inventory: find every instance of the affected product and version (include internet-facing and forgotten ones).
2. Patch or mitigate per the vendor advisory; if you cannot patch, remove internet exposure or apply the vendor workaround.
3. Assume compromise if the system was exposed before patching: hunt for the indicators in the advisory and review logs back to the disclosure date.
4. Rotate credentials and secrets stored on or used by the affected system if compromise cannot be ruled out.