August 25, 2026-KB5122385 Cumulative Update for .NET Framework 3.5 and 4.8.1 for Windows 11, version 25H2 and Microsoft server operating system 24H2

Applies To
.NET

Note

  • Release Date:
    August 25, 2026
  • Version:
    .NET Framework 3.5 and 4.8.1

The August 25, 2026 update for Windows 11, version 25H2 and Microsoft server operating system 24H2 includes security and cumulative reliability improvements in .NET Framework 3.5 and 4.8.1. We recommend that you apply this update as part of your regular maintenance routines. Before you install this update, see the Prerequisites and Restart requirement sections.

Summary

Security Improvements

There are no new security improvements in this release. This update is cumulative and contains all previously released security improvements.

Quality and Reliability Improvements

Area Improvement
.NET Fundamentals - Addresses an issue where intermittent crashes could occur in some 64-bit .NET Framework scenarios.

Known issues in this update

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

How to get this update

Install this update

Release Channel Available Next Step
Windows Update and Microsoft Update Yes Go to Settings > Update & Security > Windows Update. In the Optional updates available area, you’ll find the link to download and install the update.
Windows Update for Business Yes Go to Settings > Update & Security > Windows Update. In the Optional updates available area, you’ll find the link to download and install the update.
Microsoft Update Catalog Yes To get the standalone package for this update, go to the Microsoft Update Catalog website.
Windows Server Update Services (WSUS) No You can import this update into WSUS manually. See the Microsoft Update Catalog for instructions.

File information

For a list of the files that are provided in this update, download the file information for cumulative update.

Prerequisites

To apply this update, you must have .NET Framework 3.5 or 4.8.1 installed.

Restart requirement

You must restart the computer after you apply this update if any affected files are being used. We recommend that you exit all .NET Framework-based applications before you apply this update.

How to obtain help and support for this update