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On supported Windows releases, mount the WIM or VHD/VHDX, then enable the NetFx3 optional feature from matching installation media:
DISM /Image:C:MountOffline ^
/Enable-Feature ^
/FeatureName:NetFx3 ^
/All ^
/LimitAccess ^
/Source:D:sourcessxsThis offline workflow applies while .NET Framework 3.5 remains a Windows optional component, including Windows 10, applicable Windows Server releases, and Windows 11 through 25H2. Microsoft says Windows 11 version 26H1 (build 28000) and later cannot receive .NET Framework 3.5 through offline DISM servicing; those releases use a version-specific standalone installer instead.
What adding .NET Framework 3.5 actually does
NetFx3 is a Windows optional component, not just a conventional application package. It provides .NET Framework 3.5 and compatibility for applications built on .NET Framework 2.0 and 3.0 as well as 3.5. The payload may be absent from an image, so DISM needs Windows Update, a Features on Demand repository, or matching installation media to supply it. See Microsoft’s .NET Framework installation guidance.
The commands below target a mounted offline installation. They do not modify the technician computer unless you deliberately use /Online.
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Check release support and prepare the source
First identify the Windows release in the image and obtain a feature source appropriate for it. For Windows 10 and supported Windows Server images, the usual source is the original media’s sourcessxs directory. The source should match the target’s product family, release, architecture, language requirements, and servicing level as required by Microsoft’s deployment guidance.
- Use an administrator account on a technician computer with DISM and, if desired, the DISM PowerShell module.
- Keep a backup or working copy of the WIM or VHD/VHDX.
- Create a mount directory that exists, is empty, and has sufficient free space for the expanded image and DISM scratch data.
- Ensure the image is writable and no other process is using the mount directory.
- Have installation media or another validated feature source available before mounting.
Do not assume that an arbitrary Windows ISO is interchangeable. Microsoft warns that a mismatched source can fail installation or leave the image unsupported and unserviceable. Review the DISM deployment instructions and release guidance.
Identify a WIM edition and index
A WIM can contain several editions. List its indexes before mounting:
DISM /Get-ImageInfo /ImageFile:C:Imagesinstall.wimPowerShell provides the same information:
Get-WindowsImage -ImagePath 'C:Imagesinstall.wim'Record the index or image name that corresponds to the edition you will deploy. The command syntax is documented in DISM image-management options and Get-WindowsImage.
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- Create an empty directory:
md C:MountOffline- Mount the required index (replace
6with your index):
DISM /Mount-Image ^
/ImageFile:C:Imagesinstall.wim ^
/Index:6 ^
/MountDir:C:MountOfflinePowerShell equivalent:
Mount-WindowsImage `
-ImagePath 'C:Imagesinstall.wim' `
-Index 6 `
-Path 'C:MountOffline'The mount directory must be empty. Microsoft documents these operations in Mount and modify a Windows image and Mount-WindowsImage.
Mount a VHD or VHDX
Use index 1 for a VHD or VHDX image:
DISM /Mount-Image ^
/ImageFile:C:ImagesBaseImage.vhdx ^
/Index:1 ^
/MountDir:C:MountOfflinePowerShell:
Mount-WindowsImage `
-ImagePath 'C:ImagesBaseImage.vhdx' `
-Index 1 `
-Path 'C:MountOffline'Microsoft explicitly requires /Index:1 when mounting an image from a VHD or FFU. See the mounting documentation and Mount-WindowsImage reference.
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Enable NetFx3 from matching media
Assuming the installation media is drive D:, run:
DISM /Image:C:MountOffline ^
/Enable-Feature ^
/FeatureName:NetFx3 ^
/All ^
/LimitAccess ^
/Source:D:sourcessxsA local folder works the same way:
DISM /Image:C:MountOffline ^
/Enable-Feature ^
/FeatureName:NetFx3 ^
/All ^
/LimitAccess ^
/Source:C:SourcesSxSFor a network share:
DISM /Image:C:MountOffline ^
/Enable-Feature ^
/FeatureName:NetFx3 ^
/All ^
/LimitAccess ^
/Source:\FileServerWindowsMediasourcessxs| Switch | Purpose |
|---|---|
/Image: |
Targets the mounted offline Windows installation. |
/Enable-Feature |
Enables a Windows optional feature. |
/FeatureName:NetFx3 |
Selects .NET Framework 3.5. |
/All |
Enables required parent features. |
/LimitAccess |
Prevents fallback to Windows Update or WSUS, useful for a controlled offline operation. |
/Source: |
Identifies the payload location. |
These switches and the offline procedure are covered in Microsoft’s DISM deployment article.
Using a WIM as an alternate source
Some Windows Server scenarios support a WIM source with an image index:
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/Source:WIM:C:Sourcesinstall.wim:1Use this only after validating that the WIM contains the required payload and matches the target operating system. Microsoft’s Features on Demand guidance describes this syntax; it is not a universal substitute for the media’s sourcessxs directory.
Multilingual images
When servicing a reference image with multiple language packs, follow Microsoft’s documented media-servicing order. Installing language resources and .NET Framework 3.5 in the wrong sequence can leave .NET language resources incomplete; see the ordering notes in the DISM deployment guidance.
Verify that NetFx3 is enabled
Query the specific feature:
DISM /Image:C:MountOffline ^
/Get-FeatureInfo ^
/FeatureName:NetFx3Or list all optional features:
DISM /Image:C:MountOffline ^
/Get-Features ^
/Format:TableLook for State : Enabled; formatting varies by Windows and DISM version. PowerShell alternative:
Get-WindowsOptionalFeature `
-Path 'C:MountOffline' `
-FeatureName NetFx3Commit or discard the image safely
After verification, save the changes and dismount:
DISM /Unmount-Image ^
/MountDir:C:MountOffline ^
/CommitThe same command structure commits a WIM or VHD/VHDX. PowerShell:
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Dismount-WindowsImage `
-Path 'C:MountOffline' `
-SaveFor a WIM, you can request an integrity check:
Dismount-WindowsImage `
-Path 'C:MountOffline' `
-Save `
-CheckIntegrityTo abandon the changes instead:
Dismount-WindowsImage `
-Path 'C:MountOffline' `
-DiscardSaving, discarding, and integrity behavior are described in Dismount-WindowsImage. Do not use WIM-only options such as /Append with a VHD.
Troubleshoot failed or abandoned servicing
Check mount state first
DISM /Get-MountedImageInfoIf the image is listed and accessible, retry the feature operation or dismount it normally. If a previously mounted image became inaccessible, PowerShell’s Mount-WindowsImage -Remount can restore access. Do not delete the mount directory while DISM still considers the image mounted; removing files or mount metadata can damage the servicing environment or leave the image locked. References: DISM image-management options and Mount-WindowsImage.
0x800F081F: source files missing
- Point
/Sourceto the actualsourcessxsdirectory. - Confirm the files are present and readable.
- Use media matching the target release and servicing level.
- Confirm
/Image:references the intended mounted image. - Inspect
%WINDIR%LogsDISMdism.log.
Microsoft identifies this as CBS_E_SOURCE_MISSING; see the .NET Framework deployment error guidance.
0x800F0906: DISM could not download files
This commonly reflects missing Internet access, unavailable Windows Update, proxy or firewall restrictions, or WSUS policy. For a fully offline operation, provide matching media and use /LimitAccess.
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Review the policy controlling optional-component installation and component repair, particularly on devices configured to use WSUS. The same Microsoft error-resolution page lists the relevant causes.
0x800F0922 or an unexplained failure
There is no single universal fix. Verify source compatibility, inspect DISM and CBS logs, and check that the image is not corrupt. Microsoft’s installation guidance includes this code among possible installation errors.
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The command succeeds but the application still fails
The program may require .NET Framework 4.x, WCF activation, ASP.NET registration in IIS, or unrelated architecture, permissions, database, COM, or configuration components. Enabling NetFx3 does not guarantee compatibility with every legacy application.
Windows 11 26H1 and later: offline DISM is not supported
Starting with Windows 11 version 26H1, build 28000, Microsoft changed the delivery model:
- .NET Framework 3.5 is no longer a built-in optional Windows component.
- DISM cannot add it to an offline WIM or VHD/VHDX.
- The supported route is the release-specific standalone installer on a running Windows installation.
- ASP.NET 3.5, .NET Extensibility 3.5, and WCF activation components were removed from that release’s Features on Demand model.
Do not extract the standalone package into a WIM or attempt to inject it with DISM. Microsoft explicitly says offline installation and servicing are unsupported. Use the installer and switches documented for the exact release in Windows 11 .NET Framework 3.5 guidance and its FAQ; quiet installation supports switches such as /q and /quiet.
Applicability by Windows release
| Target image | Offline DISM with NetFx3 |
|---|---|
| Windows 10 | Supported with matching installation-media payloads. |
| Windows Server 2016 and later releases that retain the feature | Generally supported, subject to that release’s servicing rules and source availability. |
| Windows 11 21H2 through 25H2 | Supported while .NET Framework 3.5 remains an optional component. |
| Windows 11 26H1/build 28000 and later | Not supported offline; use the version-specific standalone installer on the running OS. |
| Older Windows releases | The traditional .NET Framework 3.5 SP1 installer may be relevant, but that is a different deployment path. |
Alternatives when image servicing is undesirable
Install during deployment
For releases that still expose NetFx3, a task sequence can enable it after Windows is applied. This helps when one image serves multiple builds or the correct source is selected per machine, but it adds deployment time and source availability requirements.
Install at first boot
A provisioning, startup, or configuration-management script can install the feature after Windows starts. The base image stays unchanged, but applications that launch before completion may fail.
Modernize the application
Microsoft recommends seeking an updated application that uses a newer .NET Framework or modern .NET. Where compatible, .NET Framework 4.8.1 may be an option, but the 4.x in-place product line does not automatically satisfy every dependency written for .NET Framework 2.0, 3.0, or 3.5.
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Online servicing is a different operation
For comparison, an already running supported Windows installation can use:
DISM /Online /Enable-Feature /FeatureName:NetFx3 /All/Online targets the currently running operating system and may use Windows Update or a configured repair source. It does not service a mounted VHD or WIM; use /Image: for an offline image. See Microsoft’s online and offline command guidance.
Frequently Asked Questions
Can I use a Windows 10 SxS source with a Windows 11 image?
Do not assume it will work. Microsoft requires a source compatible with the target release and warns that mismatched media can fail or leave the image unsupported. Obtain media matching the image’s product family, release, architecture, language requirements, and servicing level.
Can I add .NET Framework 3.5 directly to an unmounted WIM?
No. Mount the selected WIM index first, enable NetFx3 against the mount directory, then commit and dismount the image.
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No. NetFx3 supplies .NET Framework 3.5 compatibility, including applications built for 2.0 and 3.0. It does not install the separate 4.x product line.
Do I need WCF activation or ASP.NET as well?
Only if the application requires those components. NetFx3 alone does not guarantee WCF activation, ASP.NET registration, or other application dependencies.
How do I undo the change?
Before dismounting, use PowerShell Dismount-WindowsImage -Path 'C:MountOffline' -Discard instead of saving. If you already committed a WIM, restore the backup or service a new copy.
What index should I use for a VHD or VHDX?
Use index 1. WIM files can contain multiple indexes, so identify and select the required edition first.
The Bottom Line
For Windows releases where NetFx3 remains an optional component, the reliable sequence is: select the correct image index, mount it, use a matching sourcessxs source with /Image:, verify State : Enabled, and commit the dismount. Windows 11 26H1 (build 28000) and later require the release-specific standalone installer on a running system instead.
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