mstscax.dll

Microsoft Remote Desktop ActiveX Library (mstscax.dll)

System ProcessSafeDLL Library

CPU Usage

0-3%

Memory

30-120 MB

Location

C:\Windows\System32\mstscax.dll

Publisher

Microsoft Corporation

Quick Answer

mstscax.dll is a legitimate Microsoft system component that enables the Remote Desktop Client ActiveX functionality. It is digitally signed by Microsoft and is loaded by mstsc.exe when a remote session is used or embedded.

Is it a Virus?

✔ NO - Safe

Must be in C:\Windows\System32\mstscax.dll or C:\Windows\SysWOW64\mstscax.dll

Can I Disable?

❌ NO - Not advisable; disabling may disable Remote Desktop client functionality

Disabling mstscax.dll is not advisable; it is required by the Remote Desktop Client to render remote sessions

What is mstscax.dll?

mstscax.dll is the Microsoft Terminal Services Client ActiveX library. It provides the ActiveX control used to embed and manage Remote Desktop sessions within applications and the official Remote Desktop client. This DLL is loaded by the OS to support RDP features and is signed by Microsoft.

This DLL implements the ActiveX control for Remote Desktop, handling session negotiation, rendering, and input redirection. It works with the mstsc.exe process to provide a complete remote session experience and may be loaded on demand by host applications.

Quick Fact: mstscax.dll has supported RDP embedding since early versions of Windows and helps render remote sessions securely within host apps.

Types of mstscax Processes

RDP Client Hosting: Provides the ActiveX interface for embedding Remote Desktop within apps
Rendering / UI Hook: Renders remote session content within a window or embedded control
Session Negotiation: Participates in RDP handshake, security, and encryption negotiation
Input / Clipboard: Manages keyboard, mouse input and clipboard redirection
Security Layer: Works with Windows security to negotiate encryption and credentials
Driver/Display Integration: Integrates with display pipelines for color depth and DPI support

Is mstscax.dll Safe?

Yes, mstscax.dll is safe when it is the legitimate Microsoft file located in C:\Windows\System32\mstscax.dll or C:\Windows\SysWOW64\mstscax.dll and signed by Microsoft.

Is mstscax.dll a Virus or Malware?

The legitimate mstscax.dll is NOT a virus, but malicious files may masquerade with similar names. Always verify path and digital signatures.

How to Tell if mstscax.dll is Legitimate or Malware

File Location:: Must be in C:\Windows\System32\mstscax.dll or C:\Windows\SysWOW64\mstscax.dll. Other locations are suspicious.
Digital Signature:: Right-click the file in File Explorer -> Properties -> Digital Signatures. Should show a Microsoft Corporation signature.
Resource Usage:: Minimal constant CPU usage and memory usage; abnormal spikes when idle indicate interference.
Behavior:: mstscax.dll should only be loaded when Remote Desktop is used or embedded; persistent background loading is atypical.

Red Flags: If mstscax.dll is found outside System32/SysWOW64 or lacks a Microsoft signature, or shows abnormal CPU spikes when Remote Desktop is not in use, run a full malware scan.

Why Is mstscax.dll Running on My PC?

mstscax.dll runs to support the Remote Desktop Client when a remote session is active or when host applications embed RDP functionality. It loads as needed to render, negotiate, and manage the session securely.

Reasons it's running:

Active Remote Desktop Session: mstscax.dll is loaded to render the remote desktop session and handle user input when you connect to another machine.
Background RDP Features: Clipboard, device redirection, and audio redirection features may keep the DLL loaded for seamless operation.
Embedded Remote Desktop: Applications embedding RDP controls rely on mstscax.dll for rendering the remote session within their UI.
System Startup / Service Interactions: Remote Desktop Services components can keep related DLLs resident to enable quick session reattachment.
Security / Negotiation Activity: Security handshakes and encryption negotiation can keep the DLL loaded briefly during session setup.

Can I Disable or Remove mstscax.dll?

Disabling mstscax.dll is not recommended. It is a core component for Remote Desktop functionality; removal or disabling can break remote sessions embedded in apps or the mstsc.exe client.

How to Stop mstscax.dll

Disable Remote Desktop Client UI: In Windows Settings, disable the Remote Desktop option to prevent new sessions from starting.
Prevent mstsc.exe Launch: Disable any startup entries or scheduled tasks that launch mstsc or the Remote Desktop client.
Limit Embedding: If you control host applications, remove or disable the embedded RDP control to avoid loading mstscax.dll.
Group Policy: Use Group Policy to restrict Remote Desktop services if appropriate for your environment.
System Reconfiguration: Note that mstscax.dll is a system component; permanent removal is not supported on standard Windows installs.

How to Uninstall mstscax.dll

✔ Windows Features: Turn off Remote Desktop and related features (if available) in Settings -> Apps & Features -> Optional Features
✔ System integrity: Do not delete system DLLs; use official channels to disable features instead
✔ Consider alternatives: Use another remote access tool if Remote Desktop is not needed

Common Problems: RDP DLL Errors

If mstscax.dll is causing issues, common problems include loading errors, corruption after Windows updates, or conflicts with third-party capture or security software.

Common Causes & Solutions

Corrupted System File mstscax.dll: Run SFC and DISM; replace the dll from a healthy system if needed via Windows Update or Microsoft Fix-It tools
Windows Update conflicts: Install latest cumulative updates and reboot; ensure the update didn't corrupt RDP components
Conflicting security software: Temporarily disable antivirus/firewall to test; ensure security software isn't blocking mstscax.dll
Incorrect permission settings: Reset permissions on C:\Windows\System32\mstscax.dll to TrustedInstaller
Outdated Remote Desktop Client: Ensure Windows is updated to include the latest RDP components
Embedding application issues: If an app embedding mstscax.dll fails, update or reconfigure the host application

Quick Fixes:
1. Quick Fixes:
2. 1. Run System File Checker: sfc /scannow to repair missing or corrupted system files
3. 2. Run DISM: DISM /Online /Cleanup-Image /RestoreHealth
4. 3. Ensure Windows is up to date
5. 4. Re-register the RDP components if possible

Frequently Asked Questions

Is mstscax.dll a virus?

mstscax.dll is a legitimate Microsoft ActiveX library used by Remote Desktop Client; ensure it is located at C:\Windows\System32\mstscax.dll or C:\Windows\SysWOW64\mstscax.dll and signed by Microsoft.

What does mstscax.dll do on my PC?

mstscax.dll is loaded when you use Remote Desktop or when an application embeds the RDP ActiveX control. If not using Remote Desktop, it should not consume resources excessively.

Can I delete mstscax.dll?

mstscax.dll is part of Windows; it cannot be uninstalled independently. To disable Remote Desktop features, use Windows Settings or Group Policy to turn off the Remote Desktop client.

Can I disable mstscax.dll?

Disabling Remote Desktop features will generally prevent mstscax.dll from loading, but this will also disable remote access capabilities. Use Settings/GP to restrict usage instead of removing the DLL.

How do I fix mstscax.dll errors?

If you encounter errors, verify the file is signed by Microsoft and located in the System32 or SysWOW64 folder; run sfc /scannow and DISM to repair system files.

Why does my application fail to load mstscax.dll?

For embedded scenarios, ensure host applications are trusted and updated; conflicts with older RDP components can cause load failures.