mpasdesc.dll errors usually point to a damaged or incomplete Microsoft Defender installation, not a missing game runtime. If Windows reports that mpasdesc.dll is missing, cannot be located, or could not be loaded, repair Defender instead of downloading a replacement DLL.
Which fix applies to you
Use the description that best matches your problem:
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- The error appeared during normal Windows use: install pending Windows updates, restart, and update Defender from Windows Security.
- The file is missing from a Defender folder: run the Defender update commands, then repair Windows components with DISM and SFC.
- The error appeared while onboarding Windows Server 2012 R2 or Server 2016 to Defender for Endpoint: use Microsoft’s current onboarding package and
install.ps1. Do not copy the DLL from another computer. - Windows Security shows the file in Protection history: verify its path and signature, then restore it only if it is a genuine Microsoft Defender component.
- The file returns to quarantine or disappears after every update: run a full or offline scan and investigate Defender logs before adding exclusions.
- The error began after a device or system change: check Windows servicing and Defender first. A graphics, audio, or chipset driver is not a normal dependency of this file.
What is mpasdesc.dll
mpasdesc.dll is associated with Microsoft Defender Antivirus and related Microsoft antimalware products. Its internal description is “Definition Update Descriptions.” It is not a Visual C++ runtime, DirectX component, .NET assembly, device-driver library, or ordinary third-party application dependency.
Older Defender installations may use:
C:Program FilesWindows Defender
Current Defender platform files are commonly stored below a versioned directory such as:
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C:ProgramDataMicrosoftWindows DefenderPlatform<platform-version>
Microsoft documents both locations when describing how to locate MpCmdRun.exe and update Defender. See Microsoft’s Defender Antivirus update documentation.
A file with the correct name is not automatically trustworthy. Check that it is in a Defender directory and has a valid Microsoft digital signature.
Check the path and signature
- Open File Explorer.
- Paste this path into the address bar:
text
C:Program FilesWindows Defender
- If the file is not there, check:
text
C:ProgramDataMicrosoftWindows DefenderPlatform
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mpasdesc.dll. - Right-click the file, select Properties, and open Digital Signatures.
- Select the signature and choose Details.
- Confirm that Windows reports the signature as valid and that the signer is Microsoft.
Do not treat an old file listing that describes version 4.0.1526.0 and a size of approximately 0.14 MB as the current specification. Defender platform files vary by operating system, architecture, and installed platform package.
Fix 1: Update Defender from Windows Security
This is the safest first repair for Windows 10 and Windows 11.
- Open Start.
- Search for Windows Security and open it.
- Select Virus & threat protection.
- Under Virus & threat protection updates, select Protection updates.
- Select Check for updates.
- Wait for the update to finish.
- Restart Windows.
- Repeat the action that produced the
mpasdesc.dllerror.
If the update installs successfully and the application or Defender service starts normally, no DLL replacement is needed.
Also open Settings > Windows Update and select Check for updates. Install pending updates, restart, and check again. Defender platform updates and security-intelligence updates are delivered through supported Microsoft update channels, including Windows Update, WSUS, Configuration Manager, and Windows Security. Microsoft identifies platform updates with KB4052623 and security-intelligence updates with KB2267602.
Fix 2: Update Defender from an elevated Command Prompt
Use this when Windows Security reports an update failure or the graphical update does not restore the component.
- Open Start.
- Type Command Prompt.
- Right-click Command Prompt and select Run as administrator.
- Approve the User Account Control prompt.
- Run:
bat
MpCmdRun.exe -SignatureUpdate
- Restart Windows when the command completes.
If Windows says that MpCmdRun.exe is not recognized, run it from the Defender folder. The current platform location can be found below:
C:ProgramDataMicrosoftWindows DefenderPlatform
Open the newest platform-version folder, hold Shift, right-click an empty area, select Open in Terminal or Open PowerShell window here, and run:
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MpCmdRun.exe -SignatureUpdate
On older installations, use:
cd /d "%ProgramFiles%Windows Defender"
MpCmdRun.exe -SignatureUpdate
A successful update should complete without a missing-file error. If the command fails, continue with Windows component repair rather than copying mpasdesc.dll from another machine.
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Fix 3: Repair damaged Defender definitions
If the problem began after a failed definition update, reset the dynamic definitions and download them again.
Open Command Prompt as administrator and run these commands separately:
MpCmdRun.exe -RemoveDefinitions -DynamicSignatures
MpCmdRun.exe -SignatureUpdate
Restart Windows and test Defender.
Microsoft also documents these rollback commands:
MpCmdRun.exe -RemoveDefinitions -All
MpCmdRun.exe -RevertPlatform
MpCmdRun.exe -ResetPlatform
Use rollback commands only when the failure began immediately after a Defender update and an administrator understands the security impact. Reverting security components can temporarily reduce protection until a working update is installed.
Fix 4: Repair Windows component corruption
A damaged Windows component store can prevent Defender from installing or updating correctly.
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- Type Command Prompt.
- Select Run as administrator.
- Run this command and wait for it to finish:
bat
DISM.exe /Online /Cleanup-Image /RestoreHealth
- Then run:
bat
sfc /scannow
- Restart the computer.
- Open Settings > Windows Update and check for updates again.
- Return to Windows Security > Virus & threat protection > Protection updates and select Check for updates.
DISM should be run before SFC. If DISM cannot obtain repair files, Microsoft documents using a matching Windows installation source with /Source and /LimitAccess; the source must match the installed Windows edition and architecture.
Repeating SFC and DISM without knowing which component changed can make troubleshooting slow. Outbyte PC Repair can show what its free scan identifies, while repairs are performed by the full version; it is optional, and Microsoft’s built-in commands remain the supported first choice.
If DISM and SFC complete successfully but Defender still will not start, continue with the quarantine and server-specific checks below.
Fix 5: Check Defender quarantine
Defender or another security product may have quarantined a genuine component, although a missing file can also indicate corruption or tampering.
- Open Windows Security.
- Select Virus & threat protection.
- Select Protection history.
- Expand entries related to
mpasdesc.dll. - Check the reported path, detection name, and action.
- Restore the file only when its path and digital signature identify it as a Microsoft Defender component.
From an elevated Command Prompt, Microsoft documents:
MpCmdRun.exe -Restore -ListAll
To restore a specific item:
MpCmdRun.exe -Restore -Name <filename>
After restoration, update Defender and restart Windows. Do not add a broad exclusion merely to stop the warning. Exclusions reduce protection. If the file is repeatedly quarantined, run a Full scan and then a Microsoft Defender Offline scan from Windows Security > Virus & threat protection > Scan options.
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The Offline scan restarts Windows and checks the system before normal Windows processes load. If detections continue, investigate the detection and submit a suspected false positive through Microsoft’s supported process rather than repeatedly restoring the file.
Fix 6: Repair a Defender for Endpoint onboarding failure
Microsoft documents this specific error:
Couldn't find c:program fileswindows defendermpasdesc.dll, - 310 WinDefend
It applies particularly to Windows Server 2012 R2 and Windows Server 2016 when Defender for Endpoint onboarding follows an operating-system update or installation times out on slower disks.
For this situation:
- Obtain the latest Defender for Endpoint installation package from the Microsoft Defender portal.
- Download the current
install.ps1script with the package. - Remove any stale copy of the onboarding package.
- Restart the server if a Windows update is pending.
- Run the current script according to Microsoft’s server onboarding instructions.
- Review the onboarding output and Defender service status.
Do not resolve this error by copying mpasdesc.dll from another server. The package and script must match the product, operating system, and architecture.
Fix 7: Check architecture and related drivers
Defender update packages are available for x86, x64, and ARM systems. Use the package matching the operating system and product. Microsoft’s Defender Security Intelligence updates provide architecture-specific packages, including executable packages such as mpam-fe.exe and mpam-feX64.exe, not standalone mpasdesc.dll downloads.
You can check the system architecture under Settings > System > About > System type. Do not choose a package because an old file listing says it is 32-bit.
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Device drivers are not the normal repair route for mpasdesc.dll. If the problem appeared alongside broader hardware or Windows failures, update drivers only from the computer or device manufacturer’s official source, or through Windows Update. In Device Manager, right-click the affected device, select Update driver, and choose Search automatically for drivers.
Manually hunting through many driver versions can make it difficult to identify what changed. Outbyte Driver Updater can use its free scan to show outdated drivers, while driver installation is handled by the full version; it is optional and does not replace the Defender repair steps.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What not to do
Do not download a standalone DLL
Microsoft does not provide a supported standalone mpasdesc.dll download page. Random DLL sites cannot establish that a file matches the installed Defender platform, architecture, signing state, or Windows build. A replacement can contain malware, be the wrong version, or disappear during the next Defender update.
Use Windows Update, Windows Security, Microsoft’s Defender update packages, or the current Defender for Endpoint onboarding package instead.
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Do not place it in System32 or SysWOW64
mpasdesc.dll should not normally be placed in:
C:WindowsSystem32
C:WindowsSysWOW64
Those are generic system DLL directories, not the documented Defender locations.
Do not run regsvr32
regsvr32 is intended for DLLs that expose a DllRegisterServer entry point, typically COM-style components. Microsoft’s documented repair path for Defender is platform updating and MpCmdRun.exe, not registering this resource component. Running regsvr32 mpasdesc.dll is therefore not a routine fix.
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If the error keeps returning
If the file disappears after every Defender update:
- Check Protection history for repeated quarantine actions.
- Verify the file’s path and Microsoft signature.
- Run a Full scan and Microsoft Defender Offline scan.
- Check for pending Windows updates and restart requirements.
- Review Defender and Windows event logs for service or update failures.
- Confirm that security software or an organizational policy is not removing the component.
- Run DISM and SFC again only if Windows servicing corruption remains suspected.
System Restore may help when the failure began immediately after a recent update and a suitable restore point exists. It is a fallback, not the primary Defender repair.
Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteIf Defender remains broken after supported updates, quarantine checks, DISM, SFC, and a restart, use Windows recovery or an in-place Windows repair workflow. For managed servers or recurring Defender for Endpoint onboarding failures, escalate to Microsoft support with the onboarding logs and exact error text.
FAQ
Is mpasdesc.dll malware?
A missing file does not prove malware. A file with the correct name does not prove authenticity either. Verify its Defender path and Microsoft digital signature, then scan the system if the file is repeatedly removed.
Is mpasdesc.dll part of Windows?
It is a Microsoft Defender component delivered with Defender platform and antimalware installations. Its location can vary between the older Windows Defender directory and the versioned Defender platform directory.
Can I register it with regsvr32?
No. regsvr32 is not the documented repair method for this Defender component. Update Defender and repair Windows components instead.
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No. The copied file may not match the installed Defender platform, architecture, or Windows build, and it can be overwritten by the next update.
Does the 32-bit listing mean I need a 32-bit Windows package?
No. An old third-party metadata record is not a current package specification. Choose the Defender package that matches the operating system and product architecture.
What is the safest first step?
Install pending Windows updates, restart, and use Windows Security > Virus & threat protection > Protection updates > Check for updates. If that fails, use MpCmdRun.exe -SignatureUpdate, then DISM and SFC.
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