.NET Framework 3.5 Install Fails with Error 0x800F081F? Point It at a Real Source

Q: I get 0x800F081F even with /Source — why?

Confirm the path is exactly :\sources\sxs, that the folder really exists on the media, and that you have Read access to it. A wrong path or incomplete media is the usual cause.

Published ✓ Verified ⏱️ 2 min read March 18, 2025 · by Ryan Bennett

Turning on .NET Framework 3.5 (in Optional Features or via DISM) fails with error 0x800F081F — “The source files could not be found.”

Why: In Windows 11 and 10, .NET Framework 3.5 is a Feature on Demand — the metadata ships in Windows but the actual binaries don’t. Windows tries to fetch them from Windows Update; 0x800F081F (CBS_E_SOURCE_MISSING) means it couldn’t reach a valid source, often because a managed PC is pointed at a WSUS server or has no internet path to the payload.

Fix 1: Enable it the normal way (when Windows Update works)

Settings → System → Optional features → scroll to More Windows features.
Tick .NET Framework 3.5 (includes .NET 2.0 and 3.0), click OK.
Let Windows download the files and reboot.

If that downloads fine, you’re done. If it returns 0x800F081F, use a local source instead (Fix 2).

Fix 2: Install from Windows installation media with DISM

This is Microsoft’s recommended workaround when Windows Update can’t supply the files. You need a Windows ISO or USB matching your installed version.

Mount the Windows ISO (right-click the .iso → Mount) or insert the install USB, and note its drive letter (e.g. D:).
Open Command Prompt as administrator.
Run, substituting your drive letter for D:

Dism /online /enable-feature /featurename:NetFx3 /All /Source:D:\sources\sxs /LimitAccess

The \sources\sxs folder holds the .NET 3.5 payload. /LimitAccess tells DISM to use only your media and not contact Windows Update.

Fix 3: Managed PC pointed at WSUS — fix the Group Policy

On work machines, 0x800F081F often means feature payloads are blocked because the PC uses WSUS for servicing. An admin can allow direct download:

Open Edit group policy (gpedit.msc).
Go to Computer Configuration → Administrative Templates → System.
Open Specify settings for optional component installation and component repair → set to Enabled.
Either tick Contact Windows Update directly to download repair content instead of Windows Server Update Services (WSUS), or set the Alternate source file path to a share containing the \sources\sxs files (for example \\server\share\sxs).
Click OK, then run gpupdate /force from an admin Command Prompt and re-enable the feature.

FAQ

Which ISO do I need? One that matches your installed Windows version. A mismatched build can give the same “source missing” error.

I get 0x800F081F even with /Source — why? Confirm the path is exactly <drive>:\sources\sxs, that the folder really exists on the media, and that you have Read access to it. A wrong path or incomplete media is the usual cause.

Sources: Microsoft Learn — .NET Framework 3.5 installation errors (0x800F0906, 0x800F081F, 0x800F0907)