Patch tracker / CVE reference / CVE-2026-21253
CVE-2026-21253
CVE-2026-21253 is a high severity Microsoft vulnerability with a CVSS score of 8.8. Its EPSS score puts the probability of exploitation in the next 30 days at 26%. 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.
High severity Microsoft vulnerability, CVSS 8.8. Fixed by 14 Microsoft security updates.
Risk summary
Updated July 25, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.
Senserva AI Opinion for CVE-2026-21253
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.
Full tracking and change history for CVE-2026-21253
Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.
Exploitation and severity
Not in the CISA KEV catalog. EPSS exploit probability 26%. CVSS 8.8 (High).
This CVE is among the top half of tracked Microsoft CVEs by EPSS exploit probability.
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.
Affected products
Common questions about CVE-2026-21253
Is CVE-2026-21253 actively exploited?
It is not currently listed in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score puts the probability of exploitation in the next 30 days at 26%.
What patch fixes CVE-2026-21253?
Microsoft fixed CVE-2026-21253 in KB5075897, KB5075899, KB5075904, KB5075906, KB5075912, KB5075941, KB5075942, KB5075943, KB5075970, KB5075971, KB5075999, KB5077179, KB5077181, KB5077212. Download from the Microsoft Update Catalog, or let Intune, Windows Update, or WSUS deliver it.
Which products are affected by CVE-2026-21253?
Windows 10 Version 1809 for 32-bit Systems, Windows 10 Version 1809 for x64-based Systems, Windows Server 2019.
Can I ask my own AI about CVE-2026-21253?
Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2026-21253's key facts: severity, CVSS, EPSS exploit probability, CISA KEV status, and the fixing KB. Copy it into Claude, ChatGPT, or Copilot for a triage plan; the data is refreshed twice a day (5 AM and 3 PM US Central).
Fixed by the same updates
If you are patching CVE-2026-21253, the same updates also fix these:
Authoritative references
Want every Microsoft CVE and the patches that fix it, ranked by real-world risk? See the Microsoft Patch Tracker.
