Patch tracker / CVE reference / CVE-2026-21513
CVE-2026-21513
CVE-2026-21513 is a Microsoft vulnerability that Microsoft rates Important, with a CVSS score of 8.8 (High). It is in the CISA Known Exploited Vulnerabilities catalog: attackers are using it in the wild, which makes it a fix-first item. Microsoft has shipped the fix: deploy one of the 14 updates below from the Microsoft Update Catalog, and see where this CVE sits against the rest on the patch tracker.
Our data comes from Microsoft, CISA and other public sources, and it can be wrong or out of date. If you are unsure, check the linked source before you act, and tell us when we are wrong so we can fix it.
Microsoft rates it Important. CVSS 8.8 (High). Fixed by 14 Microsoft security updates.
Risk summary
Listed in the CISA Known Exploited Vulnerabilities catalog, confirmed exploited in the wild. EPSS exploit probability 16%. CVSS 8.8 (High).
This CVE is among the top 5% of tracked Microsoft CVEs by EPSS exploit probability, and one of 5 actively-exploited CVEs in February 2026.
CVE-2026-21513 is a MSHTML Framework security feature bypass in Windows that Microsoft rates High severity (CVSS 8.8), and CISA confirmed it is being actively exploited by adding it to the KEV catalog on 2026-02-10. Exposure spans both new Windows 11 26H1 builds (ARM64 and x64) and the older Windows 10 1809 32-bit release, so mixed-age fleets are affected. Because MSHTML bypasses are commonly chained with a document or web lure to defeat a protection users would otherwise rely on, the confirmed exploitation makes this urgent despite no ransomware link yet.
Do this: Deploy the Microsoft patches for CVE-2026-21513 to all Windows 11 26H1 (ARM64 and x64) and Windows 10 1809 32-bit systems now, prioritizing internet-facing and email-handling hosts to meet the CISA KEV timeline.
AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for CVE-2026-21513
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Official patch(es) for CVE-2026-21513
Treat as urgent: it is being exploited in the wild (CISA KEV), so patch ahead of items that are not. In Intune or Defender, confirm whether the fixing updates KB5075897, KB5075899, KB5075904, KB5075906, KB5075912, KB5075941, KB5075942, KB5075943, KB5075970, KB5075971, KB5075999, KB5077179, KB5077181, KB5077212 are installed across the affected products. Senserva does this automatically across your tenant and flags every missing patch.
Apply the Microsoft security updates below to fix CVE-2026-21513. Each KB page carries the Microsoft Update Catalog download, Microsoft's known issues for the update, a copy-paste PowerShell check for whether it is installed, and the Senserva AI read.
Scope and sources
- Affected products
- Windows 10 Version 1607 for 32-bit Systems
- Windows 10 Version 1607 for x64-based Systems
- Windows 10 Version 1809 for 32-bit Systems
- Windows 10 Version 1809 for x64-based Systems
- Windows 10 Version 21H2 for 32-bit Systems
- Windows 10 Version 21H2 for ARM64-based Systems
- Windows 10 Version 21H2 for x64-based Systems
- Windows 10 Version 22H2 for 32-bit Systems
- Windows 10 Version 22H2 for ARM64-based Systems
- Windows 10 Version 22H2 for x64-based Systems
- Windows 11 Version 23H2 for ARM64-based Systems
- Windows 11 Version 23H2 for x64-based Systems
- Windows 11 Version 24H2 for ARM64-based Systems
- Windows 11 Version 24H2 for x64-based Systems
- Windows 11 Version 25H2 for ARM64-based Systems
- Windows 11 Version 25H2 for x64-based Systems
- Windows 11 Version 26H1 for ARM64-based Systems
- Windows 11 version 26H1 for x64-based Systems
- Windows Server 2012
- Windows Server 2012 (Server Core installation)
- Windows Server 2012 R2
- Windows Server 2012 R2 (Server Core installation)
- Windows Server 2016
- Windows Server 2016 (Server Core installation)
- Windows Server 2019
- Windows Server 2019 (Server Core installation)
- Windows Server 2022
- Windows Server 2022 (Server Core installation)
- Windows Server 2022, 23H2 Edition (Server Core installation)
- Windows Server 2025
- Windows Server 2025 (Server Core installation)
- Fixed by the same updates
- Authoritative references
Want every Microsoft CVE and the patches that fix it, ranked by real-world risk? See the Microsoft Patch Tracker.