Patch tracker / KB5091596
KB5091596: ASP.NET Core 10.0 Security Update (April 2026)
KB5091596 is a Critical security update for ASP.NET Core 10.0, released 2026-04-14. It closes 1 CVE with a maximum CVSS of 9.1. It is the 48th largest of the 60 updates Microsoft shipped that month, by CVEs closed.
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Update summary
Fixes 1 CVE. Most severe CVSS 9.1 (Critical). EPSS exploit probability up to <1%. Among the lower half of tracked Microsoft updates by EPSS exploit probability.
A newer security update for ASP.NET Core 10.0 has shipped since this one: KB5130036 (2026-10-13). For cumulative update families the newer package includes these fixes, so installing that one is usually the shorter path. Verify against your own update rings before you skip this package.
KB5091596 patches CVE-2026-40372 in ASP.NET Core 10.0, rated Critical at CVSS 9.1, so any server or app running this framework version is exposed. The EPSS score of 11 percent is elevated for a fresh release and suggests exploitation is more plausible than typical, though it is not yet in CISA KEV or tied to ransomware. Because ASP.NET Core often powers internet-facing web APIs and sites, a Critical flaw here can reach externally accessible surfaces.
Do this: Inventory hosts running ASP.NET Core 10.0 and deploy KB5091596 to internet-facing web servers first.
AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for KB5091596
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for KB5091596
- Released
- 2026-04-14
- Last changed
- 2026-09-24
- Changes tracked
- 2
Senserva began recording day-to-day change history on 2026-07-07, and refreshes it several times a day. Release dates are historical where Microsoft publishes them; revision history is tracked from that date forward, so it does not include changes made before then.
Check if KB5091596 is installed
Elevated PowerShell. No output means it is not installed.
CVEs fixed by this update
Sorted exploited-first, then by CVSS. Every CVE links to its Senserva page with the full risk facts, references, and a ready-to-paste AI prompt.
| CVE | Severity | CVSS | EPSS | Exploited |
|---|---|---|---|---|
| CVE-2026-40372 | Critical | 9.1 | <1% | No |
Scope and sources
- Affected products
- Also released in April 2026
KB5082052
114 CVEs · Critical · exploitedKB5082060
120 CVEs · Critical · exploitedKB5082063
123 CVEs · Critical · exploitedKB5082123
106 CVEs · Critical · exploitedKB5082142
115 CVEs · Critical · exploitedKB5082198
86 CVEs · Critical · exploitedKB5082200
106 CVEs · Critical · exploitedKB5083768
119 CVEs · Critical · exploitedThe full month, summarized: Microsoft Patch Tuesday.
- Authoritative references
See this and every Microsoft update ranked by real-world risk on the Microsoft Patch Tracker.