Known exploited vulnerability
CVE-2026-21513
The short answer
CVE-2026-21513 affects Microsoft Windows 10 Version 1607 and is rated high (CVSS 8.8). CISA added it to the Known Exploited Vulnerabilities catalog on 2026-02-10: attackers are using it, so patch it first.
What it is
Protection mechanism failure in MSHTML Framework allows an unauthorized attacker to bypass a security feature over a network.
Weakness: CWE-693.
Severity
8.8 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Exploited (CISA KEV)
Yes, since Feb 10, 2026
Federal due date Mar 3, 2026
EPSS, next 30 days
16%
Higher than 97% of scored CVEs
How it can be exploited
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
What CISA says to do
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Affected products
Windows 10 Version 1607, Windows 10 Version 1809, Windows 10 Version 21H2, Windows 10 Version 22H2, Windows 11 version 22H3, Windows 11 Version 23H2, Windows 11 Version 24H2, Windows 11 Version 25H2, Windows 11 version 26H1, Windows 11 Version 26H1, Windows Server 2012, Windows Server 2012 (Server Core installation). NVD's record lists the exact affected versions.
References
- msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21513 Vendor Advisory
- www.vicarius.io/vsociety/posts/cve-2026-21513-detection-script-security-feature-bypass-vulnerability-in-mshtml-framework Third Party Advisory
- www.vicarius.io/vsociety/posts/cve-2026-21513-mitigation-script-security-feature-bypass-vulnerability-in-mshtml-framework MitigationThird Party Advisory
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21513 US Government Resource
Questions
Is CVE-2026-21513 being exploited?
Yes. CISA added CVE-2026-21513 to its Known Exploited Vulnerabilities catalog on 2026-02-10, with a federal remediation due date of 2026-03-03.
How do I fix CVE-2026-21513?
CISA's 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.
From NVD, CISA KEV, FIRST EPSS and OSV.dev, checked . Status on NVD: Analyzed. The description is NVD's text, quoted as published.
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