ATM Manual Review Findings

ATM-01M: Inexistent Initialization Protection of Base Implementation

Type	Severity	Location
Language Specific		ATM.sol:L12

Description:

The contract is meant to be upgradeable yet does not properly protect its logic deployment from malicious initializations.

Example:

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9contract ATM is AccessControlUpgradeable {
10    bytes32 public constant CHILD_ROLE = keccak256("CHILD_ROLE");
11
12    function initialize(address owner) public initializer {
13        __AccessControl_init();
14
15        _setupRole(DEFAULT_ADMIN_ROLE, owner);
16    }

Recommendation:

We advise a constructor to be introduced that either invokes the initializer modifier of the Initializable contract or invokes the Initializable::_disableInitializers function to prevent the base implementation from ever being initialized.

Alleviation (58e8cc66dfa900c03c47df78f5170d9960005629):

An ATM::constructor has been introduced invoking the Initializable::initialize modifier thereby preventing re-initializations as long as the contract does not utilize a versioned initialization system.

If such a system is expected, we advise the Initializable::_disableInitializers function instead.

ATM-02M: Inexplicable Fallback Function

Type	Severity	Location
Language Specific		ATM.sol:L18, L20-L22

Description:

The ATM::receive and ATM::deposit functions achieve each other's purpose, however, the ATM::deposit function mandates a non-zero msg.value while the ATM::receive function permits any value.

Example:

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18receive() external payable {}
19
20function deposit() external payable {
21    require(msg.value > 0, "ATM: deposit amount must be greater than 0");
22}

Recommendation:

We advise only either of the two implementations to be retained and the correct logic to be incorporated in it, as a function being marked as payable can accept funds without the contract having a receive function defined.

Alleviation (58e8cc66dfa900c03c47df78f5170d9960005629):

The ATM::receive function has been omitted as advised, ensuring that a single implementation for accepting native funds is present in the ATM contract.