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.NET Framework 3.5 Installation Error 0x800F081F — Feature Installation Failed

Warningsystem

Overview

Fix .NET Framework 3.5 installation error 0x800F081F when Windows cannot find the source files needed to enable the feature for legacy applications.

Key Details

  • .NET Framework 3.5 is needed by many older applications and is not installed by default on Windows 10/11
  • Error 0x800F081F means Windows cannot find the source files to install the feature
  • This commonly occurs when WSUS (Windows Server Update Services) is configured in enterprise environments
  • The feature can be installed from Windows Update, the installation media, or a downloaded package
  • .NET Framework 3.5 includes 2.0 and 3.0 — installing 3.5 covers all legacy .NET Framework versions

Common Causes

  • Group Policy configured to use WSUS which does not have the .NET 3.5 package
  • Windows Update service unable to download the required component files
  • Windows installation media or source files corrupted or unavailable
  • Previous .NET Framework installation failed and left corrupted state

Steps

  1. 1Try online installation: run 'DISM /Online /Enable-Feature /FeatureName:NetFx3 /All' as admin
  2. 2If WSUS blocks it: temporarily set Group Policy to allow Windows Update for feature installation
  3. 3Install from Windows ISO: mount ISO, run 'DISM /Online /Enable-Feature /FeatureName:NetFx3 /Source:D:\sources\sxs /LimitAccess'
  4. 4Check Windows Update settings: ensure the PC can reach Windows Update servers directly
  5. 5Run Windows Update troubleshooter if the online installation method fails

Tags

dotnetframework-3.50x800f081ffeatureinstallation

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Frequently Asked Questions

Windows 10/11 includes .NET 4.x by default. .NET 3.5 is an older framework kept as an optional feature for backward compatibility with legacy applications. It is installed on demand when an app requires it.