The Problem

.NET Framework 3.5 is not shipped in the Windows 11 install image. It is an on-demand feature, so when an older program asks for it, Windows must download the files from Windows Update. If that download is blocked — by policy, by a WSUS server, or by a broken update stack — the install fails with a code rather than a useful message.

The fix is either to unblock the download or to install the feature offline from the Windows installation media, which needs no internet at all and works when everything else fails.

Program reports a missing DLL instead? Different runtime — see fix VCRUNTIME140.dll missing and fix MSVCP140.dll missing.

Symptoms

Error 0x800F0950 — "Windows couldn't complete the requested changes."
Error 0x800F081F — "The source files could not be found."
Error 0x800F0954 on a domain-joined or work PC.
The feature dialog spins on "Downloading required files" and then fails.
An older program refuses to start, naming .NET Framework 3.5.

Step 1: Try the Normal Route Once

Worth 60 seconds before anything else.

Press Windows + R, type optionalfeatures.exe, press Enter.
Tick .NET Framework 3.5 (includes .NET 2.0 and 3.0).
Click OK → Let Windows Update download the files for you.
If it completes, you are done. If it errors, note the code and continue.

Step 2: Install It Offline from the Windows ISO

This is the reliable method and the one to use when the error is 0x800F081F.

Download the Windows 11 Disk Image (ISO) from Microsoft's official download page.
Right-click the ISO in File Explorer → Mount. Note the drive letter it is given, for example E:.
Right-click Start → Terminal (Admin).

Run, replacing E: with your mounted letter:

DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:E:\sources\sxs

Wait for The operation completed successfully, then reboot.
Eject the ISO afterwards: right-click the drive in File Explorer → Eject.

If the ISO version does not match your installed build, the operation can still fail. Use an ISO of the same Windows 11 version — check yours with Windows + R → winver.

Step 3: Remove the Group Policy Block

Error 0x800F0954 almost always means policy is forcing the PC to use an internal update server that does not have the feature.

Press Windows + R, type gpedit.msc, press Enter. (On Windows 11 Home this is absent — use Step 4 instead.)
Go to Computer Configuration → Administrative Templates → System.
Open Specify settings for optional component installation and component repair.
Set it to Enabled, then tick Download repair content and optional features directly from Windows Update instead of Windows Server Update Services (WSUS).
Click OK, then in Terminal (Admin) run:
```
gpupdate /force
```
Retry Step 1.
On a work or school PC, stop here and contact IT. That policy is deliberate, and changing it may violate your organisation's rules.

Step 4: Set the Registry Value on Windows 11 Home

Home has no Group Policy Editor, so set the value directly.

Open Terminal (Admin) and run:

reg add "HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU" /v UseWUServer /t REG_DWORD /d 0 /f

Restart the update service:
```
net stop wuauserv
```
```
net start wuauserv
```
Retry the feature install.
This only affects machines where a WSUS policy was set. On a normal home PC the key will simply be created and do nothing harmful.

Step 5: Repair the Windows Update Stack

A broken update component blocks the download regardless of policy.

In Terminal (Admin), run:

DISM /Online /Cleanup-Image /RestoreHealth

sfc /scannow

Then reset the update components:

net stop wuauserv

net stop bits

ren C:\Windows\SoftwareDistribution SoftwareDistribution.old

net start bits

net start wuauserv

Reboot and retry.
Full procedure: fix Windows 11 update errors and fix Windows Update stuck.

Step 6: Check Antivirus and the Connection

Pause any third-party security suite and retry the install. Several block DISM's access to the component store.
If you are on a VPN or a filtered network, disconnect and retry — the download comes straight from Microsoft's servers: set up a VPN in Windows 11.
Confirm the connection is stable: fix DNS_PROBE_FINISHED_NO_INTERNET.

Step 7: Verify the Install and Confirm the Program Works

Reopen Windows + R → optionalfeatures.exe and confirm .NET Framework 3.5 is ticked.
Or check from Terminal (Admin):
```
DISM /Online /Get-FeatureInfo /FeatureName:NetFx3
```
State : Enabled is what you want.
Install pending updates afterwards — .NET receives its own security patches: Settings → Windows Update → Check for updates.
Related: keep your devices updated safely.

Step 8: Remove and Reinstall the Feature

If the program still fails with .NET 3.5 apparently installed, the install is partial.

In Terminal (Admin):

DISM /Online /Disable-Feature /FeatureName:NetFx3 /Remove

Reboot.
Reinstall from the mounted ISO as in Step 2.
If the app still fails: fix an app crashing or not opening.

What Not to Do

Don't download a ".NET Framework 3.5 offline installer" from a third-party site. The only legitimate offline source is the sources\sxs folder in a genuine Windows ISO — see avoid malware in fake downloads.
Don't delete SoftwareDistribution outright. Rename it as shown, so Windows can rebuild and you can revert.
Don't change WSUS policy on a work machine. Ask IT to publish the feature instead.

Still Not Working?

If DISM fails from a matching ISO with policy cleared, the component store is damaged in a way RestoreHealth cannot repair. Run DISM against the ISO as a source for the repair itself:

DISM /Online /Cleanup-Image /RestoreHealth /Source:WIM:E:\sources\install.wim:1 /LimitAccess

If that also fails, an in-place repair install rebuilds the component store while keeping files and programs: reinstall Windows without losing data.

Fix .NET Framework 3.5 Install Error in Windows 11