Fix CS2 'VAC was unable to verify your game session'

Updated: 11/29/2025

You queue for a Premier match, and the red text appears instantly: 'Matchmaking Failed: VAC was unable to verify your game session'. You aren't cheating, and you have never modified game files, yet Valve is blocking you. This error happens when the Steam client loses its secure handshake with the CS2 executable, often due to a background crash of the Steam Service or a corrupted signature file.

Table of Contents

Method 1: Repair the Steam Service (The Expert Fix)

Most people verify game files, but that rarely works for this specific error. You need to repair the Steam background service itself.

Step 1: Close Steam

Right-click Steam in the taskbar and click Exit. It must be fully closed.

Step 2: Run Command

Press Win + R. Copy and paste this exact command:

"C:\Program Files (x86)\Steam\bin\SteamService.exe" /repair

Click OK. A command window will pop up and close quickly. Now run Steam as Administrator and try again.

Method 2: Verify Integrity of Game Files

If a specific DLL file got corrupted by a disk cleanup tool, VAC will flag it.

  • Go to your Steam Library.
  • Right-click Counter-Strike 2 > Properties.
  • Select Installed Files tab.
  • Click Verify integrity of game files.
Wait: Let it reach 100%. If it says '3 files failed to validate', Steam will re-download the clean versions automatically.

Method 3: Change Steam Profile Name

This sounds like a myth, but it forces a session refresh on the backend.

Go to your Steam Profile > Edit Profile. Change your Profile Name slightly (add a character or change a letter). Save changes. Sign out of Steam and sign back in. This forces the authentication server to issue a new token for your session.