Patch tracker / CVE reference / CVE-2026-21253
CVE-2026-21253
CVE-2026-21253 is a Microsoft vulnerability that Microsoft rates Important, with a CVSS score of 7.0 (High). Its EPSS score puts the probability of exploitation in the next 30 days at 25%. 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.
Risk summary
Not in the CISA KEV catalog. EPSS exploit probability 25%. CVSS 7.0 (High).
This CVE is among the top 25% of tracked Microsoft CVEs by EPSS exploit probability.
Mailslots are an old inter-process communication mechanism in Windows still used by some legacy line-of-business software, and a flaw there carries a 26 percent EPSS score, affecting Windows 11 26H1 and Windows Server 2022. Because mailslot usage is relatively uncommon today, the exposure is more about whichever legacy applications on a given server still rely on it. No confirmed exploitation or ransomware use.
Do this: Patch this on Server 2022 hosts and check whether any legacy applications there still depend on mailslot communication.
AI-generated from public data, 2026-07-07. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for CVE-2026-21253
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Official patch(es) for CVE-2026-21253
Elevated priority: high severity or a meaningful exploitation probability, sooner if an affected product is internet-facing. 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-2026-21253. 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.