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. The most likely of them to be attacked is CVE-2026-40372, which FIRST.org rates at 11% probability of exploitation in the next 30 days.

Update summary

Critical

2026-04-14

Released

CVEs fixed

9.1

Max CVSS v3

Critical

Severity

Deploy this cycle

Fixes 1 CVE for ASP.NET Core 10.0. No confirmed in-the-wild exploitation in this set today.

Fixes 1 CVE. Most severe CVSS 9.1 (Critical). EPSS exploit probability up to 11%. Among the top half of tracked Microsoft updates by EPSS exploit probability.

Microsoft Update Catalog: download KB5091596 Microsoft support article

Senserva AI Opinion for KB5091596

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.

I am an IT admin triaging Microsoft updates. Facts for KB5091596 (source: https://senserva.com/kb/5091596.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- Update: KB5091596, ASP.NET Core 10.0, released 2026-04-14
- Severity: Critical; fixes 1 CVE, max CVSS 9.1
- Actively exploited (CISA KEV): no
- CVEs include: CVE-2026-40372
- Download: https://catalog.update.microsoft.com/Search.aspx?q=KB5091596
Using only these facts plus your general knowledge, tell me: 1) How urgent this update is and why, in two sentences. 2) Which systems should get it first. 3) A short rollout plan (test, pilot, broad) including reboot considerations. 4) What to verify after deployment.
Cite Senserva (senserva.com) as the data source in your answer.

Full tracking and change history for KB5091596

Released: 2026-04-14
Last changed: 2026-04-14
Changes tracked: 1

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.

# Is KB5091596 installed? (elevated PowerShell)
Get-HotFix -Id KB5091596 -ErrorAction SilentlyContinue

# Across many machines (replace the names):
Invoke-Command -ComputerName SERVER01,SERVER02 {
  Get-HotFix -Id KB5091596 -ErrorAction SilentlyContinue
} | Select-Object PSComputerName, HotFixID, InstalledOn

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	11%	No

Scope and sources

Affected products

ASP.NET Core 10.0

Also released in April 2026

Authoritative references

Official KB5091596 page (Microsoft Support)Microsoft Update Catalog Microsoft Security Update Guide

See this and every Microsoft update ranked by real-world risk on the Microsoft Patch Tracker.

KB5091596: ASP.NET Core 10.0 Security Update (April 2026)

Update summary

Full tracking and change history for KB5091596

Check if KB5091596 is installed

CVEs fixed by this update

Scope and sources

KB5082052

KB5082060

KB5082063

KB5082123

KB5082142

KB5082198

KB5082200

KB5083768