MorpheusAI
MorpheusAI
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Submission Details
Severity: low
Valid

L1Sender does not implement `supportsInterface` function

timenov

Summary

The contracts MOR, L2TokenReceiver and L1Sender inherit ERC165. This standard is used to publish and detect what interfaces a smart contract implements. Read this for more. If we take a look at MOR and L2TokenReceiver, we can see that they implement this standard the correct way:

// MOR.sol
​
function supportsInterface(bytes4 interfaceId_) external pure returns (bool) {
return
interfaceId_ == type(IMOR).interfaceId ||
interfaceId_ == type(IERC20).interfaceId ||
interfaceId_ == type(IERC165).interfaceId;
}
// L2TokenReceiver.sol
​
function supportsInterface(bytes4 interfaceId_) external pure returns (bool) {
return interfaceId_ == type(IL2TokenReceiver).interfaceId || interfaceId_ == type(IERC165).interfaceId;
}

But there is no such function in L1Sender.sol.

Vulnerability Details

Having no supportsInterface function, means that the ERC165 standard is not implement correctly. This contract implements IL1Sender and ERC165. Lets say someone wants to check if this contract implements the IL1Sender interface. The lack of supportsInterface function, means that the return value will be false, which is wrong.

Impact

When supportsInterface is called, the output will always be false.

Proof of Concept

Do the following changes to L1Sender.sol:

  • Import the IERC165 interface at the top of the file:

import {ERC165, IERC165} from "@openzeppelin/contracts/utils/introspection/ERC165.sol";

  • Create the following pure functions:

function getL1SenderInterface() external pure returns (bytes4) {
return type(IL1Sender).interfaceId;
}
​
function getIERC165Interface() external pure returns (bytes4) {
return type(IERC165).interfaceId;
}

Full file can be found in this Gist.

Now add the following test cases to L1Sender.test.ts

describe('supportsInterface', () => {
it('should support l1Sender interface', async () => {
const l1SenderInterfaceId = await l1Sender.getL1SenderInterface();
expect(await l1Sender.supportsInterface(l1SenderInterfaceId)).to.be.true;
});
​
it('should support IERC165 interface', async () => {
const erc165InterfaceId = await l1Sender.getIERC165Interface();
expect(await l1Sender.supportsInterface(erc165InterfaceId)).to.be.true;
});
});

Run npx hardhat test.

L1Sender
supportsInterface
1) should support l1Sender interface
✔ should support IERC165 interface

As we can see, the first test fails(which is the IL1Sender) and the second(IERC165) passes. The second passes because in ERC165 the supportsInterface functions is this:

function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
return interfaceId == type(IERC165).interfaceId;
}

However this is not the expected behaviour. Both of the tests should pass.

Tools Used

Manual Review, Hardhat

Recommendations

Make sure to implement correctly the supportsInterface function:

function supportsInterface(bytes4 interfaceId_) public override pure returns (bool) {
return interfaceId_ == type(IL1Sender).interfaceId || interfaceId_ == type(IERC165).interfaceId;
}

Note that we add a check for IERC165 here as well, because this function is override.

Now run npx hardhat test again:

L1Sender
supportsInterface
✔ should support l1Sender interface
✔ should support IERC165 interface
Updates

Lead Judging Commences

hans Lead Judge almost 2 years ago
Submission Judgement Published
Validated
Assigned finding tags:

L1Sender doesn't properly implement ERC165 because it lacks `supportsInterface` function.

timenov Submitter
almost 2 years ago
inallhonesty Lead Judge
almost 2 years ago
timenov Submitter
almost 2 years ago
inallhonesty Lead Judge
almost 2 years ago
hans Lead Judge almost 2 years ago
Submission Judgement Published
Validated
Assigned finding tags:

L1Sender doesn't properly implement ERC165 because it lacks `supportsInterface` function.

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