VAC also known as Valve Anti-Cheat is a mechanism on Steam client that prevents execution of cheats like maphack, wallhack, aimbot on Valve’s multiplayer games such as CS:Go and Dota 2. Despite having strict measures, the Counter Strike Global Offensive’s casual and competitive matches are filled with cheaters who ruin experience for other players.
The VAC system is a hit or miss when it comes to catching cheaters. In addition, sometimes it prevents clean players from finding a match, prompting a false positive / error.
The other day, I was trying to find Casual mode (Deathmatch) game, I was greeted with a “Matchmaking Failed, VAC was unable to verify your game session“. To be honest, I was confused because I never use any 3rd party programs or scripts while I’m gaming. I looked for various solutions, almost every site said to Verify Integrity of Game Files through game properties but it didn’t work. I also deleted the Workshop maps but no dice. Now comes the working solution of this problem.
Update 29th March 2023 – More fixes available
After the arrival of Counter Strike 2 (CS2), many people are facing this error. I have updated more fixes you can try.
Switch your PC’s Internet Connection
Try switching your PC’s internet temporarily to 5G/4G LTE hotspot and exit steam client and try to re-login. We’re doing this because broadband internet providers (ISPs) allot single IP address (CGNAT) to multiple customers. When multiple users from same IP address try to connect same server, this could be marked as suspicious activity by Valve servers. If switching internet connection is not possible, try restarting your router/modem for refreshed IP address.
Temporarily pause Antivirus programs, Malwarebytes etc.
This may sound stupid but it works. Sometimes virus scanners start scanning the game files which makes Valve anti-cheat system to go crazy. You can temporarily pause the protection and restart Steam client to check if the error goes away.
How to fix Matchmaking Failed, VAC was unable to Verify your Game Session
1. Close any apps or games you are running and exit Steam client.
2. Right-click Start Menu, click Run. Copy-paste the following command as it is and click OK.
"C:\Program Files (x86)\Steam\bin\SteamService.exe" /repair
UAC (User Access Control) will ask permissions for Steam Client Service to repair files. Click Yes
Steam repair process will start. A blank command prompt window will appear temporarily and close itself.
3. [IMPORTANT STEP] Now temporarily disable Avast, AVG, Avira, Kaspersky, Malwarebytes or any other antivirus that you are running. You can do so by right-clicking their taskbar icon. The logic behind this is, AV programs keep scanning/inspecting executable files types which trigger Valve’s VAC system. For a permanent fix, you can add csgo.exe application to whitelist from settings.
4. Optionally, you can check CSGO for missing files just to be on the safe side.
Steam Library > Right-click CS:GO > Properties > Local Files (tab) > Verify Integrity of Game Files
If Steam finds incomplete or missing files in CS:GO’s steamapps directory, it will start reacquiring those files from Steam CDN.
5. Run Steam Client as Administrator
If you are running as Guest account or non-administrator account in Windows 10. It would be wise to run Steam as administrator. This would fix the file permissions and fix background configurations.
Right-click Steam shortcut on desktop > Run As Administrator
6. Reset CS:GO Settings
Open the properties of CS:GO, click Set Launch Options, copy this into the launch options text box and click OK.
Note: This will reset game resolution, graphics settings, key-bindings, crosshair and everything to default presets.