“authhostproxy.dll is missing” on Windows
You may see messages such as:
- “The program can’t start because authhostproxy.dll is missing from your computer.”
- “authhostproxy.dll was not found.”
- “Error loading authhostproxy.dll.”
- “authhostproxy.dll could not be loaded.”
- “authhostproxy.dll is either not designed to run on Windows or it contains an error.”
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authhostproxy.dll is the Web Authentication Host Proxy, a Microsoft Windows component associated with the Web Authentication Broker used by Windows apps for web-based sign-in. It is not a Visual C++ Redistributable, DirectX file, .NET runtime, game component, or normal driver.
Do not download a replacement DLL from a random download site. The correct file depends on your Windows release, servicing level, and system architecture. Repair Windows first.
Which fix applies to you
Use this list to choose the shortest safe path:
- The error appears in several apps or Windows sign-in features: install Windows updates, then run DISM and SFC.
- The problem started after an update, upgrade, rollback, or forced shutdown: finish Windows Update and consider Windows 11’s repair reinstall option.
- Only one Microsoft Store app fails: repair, reset, or reinstall that app.
- Only one third-party program fails: repair or reinstall that program from its official publisher or launcher.
- Windows Security quarantined the file: inspect Protection history before restoring anything.
- The file exists outside the Windows directory or has an invalid signature: treat it as suspicious and scan the system.
- SFC repeatedly reports corruption or other files disappear: back up your data and investigate storage health.
- The message remains after Windows repair: use System Restore, a repair reinstall, or installation-media recovery.
Where authhostproxy.dll should be
On 64-bit Windows, the normal 64-bit copy is generally located at:
%windir%System32AuthHostProxy.dll
The 32-bit copy used by 32-bit processes on 64-bit Windows is generally located at:
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%windir%SysWOW64AuthHostProxy.dll
On 32-bit Windows, the system copy is normally under System32.
The names are confusing: on 64-bit Windows, System32 contains 64-bit system files and SysWOW64 contains 32-bit system files. Do not copy a file between these folders based only on the folder name.
Microsoft servicing records group AuthHostProxy.dll with AuthHost.exe and AuthBroker.dll, as well as Windows Store and web-authentication components. File versions and sizes vary between Windows releases and updates, so there is no universal latest DLL to download. See Microsoft’s Web Authentication troubleshooting documentation and Windows servicing file list.
Fix 1: Install Windows updates
A missing or damaged Windows component is the most likely cause.
- Open Start.
- Select Settings.
- Open Windows Update.
- Select Check for updates.
- Install every available update.
- Restart the computer, even if Windows does not immediately require it.
- Test the app or sign-in flow again.
If the update fails, restart once more and check Windows Update again. An interrupted servicing operation can leave a component incomplete.
On eligible Windows 11 installations, you may also see Fix problems using Windows Update:
- Open Start > Settings.
- Select System > Recovery.
- Find Fix problems using Windows Update.
- Select Reinstall now.
- Follow the prompts and keep the computer connected to power.
Microsoft says this reinstalls the current Windows version while preserving apps, files, and settings. Review the recovery screen before proceeding.
Fix 2: Run DISM, then SFC
DISM repairs the Windows component store. SFC then uses that repaired store to check protected system files. Run them in this order.
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Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →- Open Start.
- Type
Command Prompt. - Right-click Command Prompt.
- Select Run as administrator.
- Approve the User Account Control prompt.
- Run:
DISM.exe /Online /Cleanup-Image /RestoreHealth
Wait for DISM to finish. It may appear paused for a while. Then run:
sfc /scannow
Restart Windows after both commands complete.
A successful SFC result usually says that Windows Resource Protection did not find any integrity violations, or that it found corrupt files and repaired them. Test the original program afterward.
If SFC says it could not repair some files, save its details:
findstr /c:"[SR]" %windir%LogsCBSCBS.log >"%userprofile%Desktopsfcdetails.txt"
Open sfcdetails.txt from the desktop and keep it for troubleshooting. Do not copy a DLL from another computer as the next step. The other computer may have a different Windows build or architecture.
Running DISM and SFC repeatedly without knowing what changed can make troubleshooting slow and inconclusive. Outbyte PC Repair can show what it identifies during its free scan, while repairs are handled by the full version, but Windows Update and Microsoft’s DISM/SFC process remain the primary repair path.
For Microsoft’s command sequence, follow the System File Checker repair instructions.
Fix 3: Repair the affected Windows app
If the error appears only when opening a Microsoft Store app, repair that app before changing system files.
- Open Start > Settings.
- Select Apps > Installed apps.
- Find the affected app.
- Select its three-dot menu.
- Choose Advanced options.
- Select Repair.
- Launch the app again.
Repair preserves the app’s data in most cases. If it does not help, return to the same screen and select Reset. Reset can remove the app’s local data. You can also uninstall and reinstall the app through Microsoft Store.
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Use Microsoft’s app repair instructions and Microsoft Store troubleshooting guidance.
If only one Windows user profile has the problem, test the app from another profile. A profile-specific authentication state can fail even when the system component is intact.
The Web Authentication Broker also has an operational log:
- Press Win+R.
- Type
eventvwr.msc. - Press Enter.
- Open Applications and Services Logs.
- Look for Microsoft > Windows > WebAuth > Operational.
Use the timestamps from the failed sign-in to identify related events.
Fix 4: Repair a third-party program
If a third-party application displays the message, do not assume that authhostproxy.dll belongs in that program’s installation folder. The application may be calling a Windows authentication component, or it may be reporting a different missing dependency under the same launch failure.
Try the program’s own repair option first:
- Open Start > Settings.
- Select Apps > Installed apps.
- Select the program’s three-dot menu.
- Choose Modify, Repair, or Advanced options, if available.
- Restart Windows and test it.
If no repair option exists, uninstall the program, restart, and reinstall it from the publisher’s official installer or launcher. Back up application settings and saved data before uninstalling.
If a game launcher reports the file inside the game directory, use the launcher’s Verify files or equivalent feature before replacing anything manually. That verifies the game installation, but it does not prove that the DLL is a game file. If the error remains, repair Windows as described above.
Common Visual C++ packages, DirectX, and .NET repairs are appropriate only when the program identifies one of those runtimes as the failing dependency. Installing them will not normally restore this Windows authentication component.
Check antivirus quarantine before restoring anything
Security software may remove or quarantine a damaged, altered, or falsely detected system file.
- Open Start.
- Search for Windows Security and open it.
- Select Virus & threat protection.
- Open Protection history.
- Review entries involving
AuthHostProxy.dll. - Note the detected path and detection name.
Restore the item only if the path is the expected Windows directory and you can verify that it is a genuine Microsoft-signed file. Microsoft warns that restoring a quarantined item puts it back on the device and may cause the detection to return. Update Defender definitions and run a scan first. If the detection remains, use Microsoft Defender Offline rather than adding an exclusion.
A copy in a downloads folder, temporary directory, application folder, or user profile is not automatically malware, but it deserves verification.
Verify the path, signature, architecture, and version
To inspect the file:
- Open File Explorer.
- Enter
%windir%System32in the address bar. - Search for
AuthHostProxy.dll. - Right-click the file and select Properties.
- Check the Digital Signatures tab.
- Select the signature and choose Details.
- Confirm that Windows reports a valid Microsoft signature.
- Review the Details tab for the file version and architecture information available on your build.
Repeat the check in %windir%SysWOW64 if you are troubleshooting a 32-bit application on 64-bit Windows.
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Do not use regsvr32 as the normal fix
regsvr32 registers DLLs that provide the appropriate COM registration entry points. It is not a general missing-DLL repair command.
Do not routinely run:
regsvr32 AuthHostProxy.dll
Registration will not repair a missing dependency, incorrect architecture, corrupted component store, invalid system file, or damaged Windows servicing state. Use Windows Update, DISM, SFC, or Windows recovery instead. Microsoft documents the command’s actual purpose in its regsvr32 reference.
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Drivers and Windows Features
Drivers are not a normal source of AuthHostProxy.dll. Do not use Device Manager as the first repair method unless Windows diagnostics identify a separate driver problem.
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If a display, storage, network, or security driver was recently changed and broader system problems appeared:
- Right-click Start.
- Select Device Manager.
- Expand the relevant device category.
- Right-click the device.
- Select Properties > Driver.
- Review the driver provider and date.
- Use Update Driver only when a suitable update is available from Windows Update or the hardware manufacturer.
- Restart Windows and retest.
Do not enable or disable random Windows Features to replace this DLL. Features such as .NET Framework or legacy components do not normally provide AuthHostProxy.dll.
Manually checking dozens of driver versions can be tedious, especially after a clean installation. Outbyte Driver Updater can show what its free scan identifies, while driver installation is handled by the full version, but use the hardware manufacturer or Windows Update when you know the affected device.
Why manual DLL downloads are unsafe
Do not download authhostproxy.dll from a DLL repository and copy it into System32, SysWOW64, an application folder, or a game folder.
That approach can introduce:
- The wrong Windows build
- The wrong 32-bit or 64-bit architecture
- An unsigned or altered binary
- Incorrect permissions and servicing metadata
- Missing dependent files
- Malware
There is no single compatible “latest AuthHostProxy.dll” for every Windows installation. The safe sources are Windows Update, Windows component repair, a Microsoft recovery process, matching installation media, or a properly created system image. A controlled replacement from matching installation media is an advanced recovery operation, not the normal consumer fix.
Recovery when the error remains
If updates, DISM, SFC, and app repair do not resolve the problem, choose the least destructive recovery option:
- System Restore: Use this if the error began after a recent system change and a restore point exists. It normally rolls back system files and settings without removing personal files.
- Windows 11 repair reinstall: Use Settings > System > Recovery > Fix problems using Windows Update > Reinstall now, when available.
- Installation-media repair: Use matching Windows installation media and follow Microsoft’s repair-installation guidance.
- Reset this PC: Use only after backing up important files and reviewing whether apps and personal data will be removed.
Use Microsoft’s Windows recovery options before choosing a destructive reset.
FAQ
Is authhostproxy.dll a Microsoft file?
Yes. It is associated with the Windows Web Authentication Host Proxy and the Web Authentication Broker.
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No. Those runtimes do not normally provide this Windows authentication component.
Which Windows versions contain it?
Microsoft servicing records include it across Windows releases, but the exact version, size, and path details depend on the release and servicing level. Do not use a file from another Windows build as a universal replacement.
Should I copy it into the program’s folder?
No. Repair Windows or repair the affected application instead. Copying a system DLL can create an architecture or servicing mismatch.
Does regsvr32 fix it?
Not normally. This is a Windows-serviced component, so registration is not the standard repair.
What if antivirus removed it?
Check Protection history, verify the file’s location and Microsoft signature, update security definitions, and scan the computer. Do not whitelist an unverified copy.
What if only one program fails?
Repair or reinstall that program from its official source, then run Windows Update and DISM/SFC if the program depends on Windows authentication.
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