Patch tracker / KB5126049

KB5126049: .NET 8.0 installed on Windows Security Update (September 2026)

KB5126049 is a High security update for .NET 8.0 installed on Windows, released 2026-09-08. It closes 2 CVEs with a maximum CVSS of 8.8. It is the 39th largest of the 60 updates Microsoft shipped that month, by CVEs closed.

Update summary

High

2026-09-08

Released

CVEs fixed

8.8

Max CVSS v3

High

Severity

Deploy this cycle

Fixes 2 CVEs for .NET 8.0 installed on Windows. No confirmed in-the-wild exploitation in this set today.

Fixes 2 CVEs. Most severe CVSS 8.8 (High). EPSS exploit probability up to <1%. Among the lower half of tracked Microsoft updates by EPSS exploit probability.

Senserva found thisread these before you deploy broadly

Microsoft documents 1 known issue with this update.

Microsoft is not currently aware of any issues in this update.

The full text, quoted from Microsoft

Microsoft Update Catalog: download KB5126049 Microsoft support article

Senserva AI Opinion and rich prompt for KB5126049

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 KB5126049 (source: https://senserva.com/kb/5126049.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed once a day (early morning US Central)):
- Update: KB5126049, .NET 8.0 installed on Windows, released 2026-09-08
- Severity: High; fixes 2 CVEs, max CVSS 8.8
- Actively exploited (CISA KEV): no
- CVEs include: CVE-2026-62886, CVE-2026-69522
- Download: https://catalog.update.microsoft.com/Search.aspx?q=KB5126049
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 KB5126049

Released: 2026-09-08
Last changed: 2026-09-10
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 KB5126049 is installed

Elevated PowerShell. No output means it is not installed.

# Is KB5126049 installed? (elevated PowerShell)
Get-HotFix -Id KB5126049 -ErrorAction SilentlyContinue

# Across many machines (replace the names):
Invoke-Command -ComputerName SERVER01,SERVER02 {
  Get-HotFix -Id KB5126049 -ErrorAction SilentlyContinue
} | Select-Object PSComputerName, HotFixID, InstalledOn

Known issues, from Microsoft

Quoted from Microsoft's support article for KB5126049 (checked 2026-09-09). Verify against the article before acting.

Microsoft is not currently aware of any issues in this update.

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-2026-69522	High	8.8	1.8%	No
CVE-2026-62886	High	7.8	1.7%	No

Scope and sources

Affected products

Also released in September 2026

Authoritative references

Official KB5126049 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.

KB5126049: .NET 8.0 installed on Windows Security Update (September 2026)

Update summary

Full tracking and change history for KB5126049

Check if KB5126049 is installed

Known issues, from Microsoft

CVEs fixed by this update

Scope and sources

KB5122871

KB5122876

KB5122878

KB5122880

KB5122882

KB5123065

KB5123066

KB5123099