Frida Game Hacking MCP

Instructions

Replace a function to always return a specific value.

Args:
    address: Address of function to replace
    return_value: Value to return

Returns:
    Replacement status.

Implementation Reference

• src/frida_game_hacking_mcp/server.py:1582-1626 (handler)

  Implements the replace_function MCP tool using Frida Interceptor.replace to override a native function to always return a specified value. Stores the hook in session state.

  @mcp.tool()
  def replace_function(address: str, return_value: Union[int, str] = 0) -> Dict[str, Any]:
      """
      Replace a function to always return a specific value.
      
      Args:
          address: Address of function to replace
          return_value: Value to return
      
      Returns:
          Replacement status.
      """
      global _session
      
      if not _session.is_attached():
          return {"error": "Not attached. Use attach() first."}
      
      if address in _session.hooks:
          return {"error": f"Hook exists at {address}. Use unhook_function() first."}
      
      try:
          addr = int(address, 16) if isinstance(address, str) and address.startswith("0x") else int(address)
          ret_val = int(return_value, 16) if isinstance(return_value, str) and return_value.startswith("0x") else int(return_value)
          
          script_code = f"""
          Interceptor.replace(ptr("{hex(addr)}"), new NativeCallback(function() {{
              return {ret_val};
          }}, 'int', []));
          send("Function replaced");
          """
          
          script = _session.session.create_script(script_code)
          script.on('message', lambda m, d: None)
          script.load()
          
          _session.hooks[address] = HookInfo(
              address=address, script=script, hook_type="replace",
              description=f"Returns {ret_val}"
          )
          
          return {"success": True, "address": address, "return_value": ret_val}
      
      except Exception as e:
          return {"error": f"Failed to replace function: {str(e)}"}