Signature malleability issue

[c4-submissions]

Lines of code

https://github.com/code-423n4/2023-10-badger/blob/main/packages/contracts/contracts/EBTCToken.sol#L218

Vulnerability details

Impact

ecrecover() is vulnerable to signature malleability.Attackers can compute a valid signature without knowing the signer's private key

Proof of Concept

The elliptic curve used in Ethereum for signatures is symmetrical, hence for every [v,r,s] there exists another [v,r,s] that returns the same valid result. Therefore two valid signatures exist which allows attackers to compute a valid signature without knowing the signer's private key. ecrecover() is vulnerable to signature malleability so it can be dangerous to use it directly.

 function permit(
        address owner,
        address spender,
        uint256 amount,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external override {
        require(deadline >= block.timestamp, "EBTC: expired deadline");
        bytes32 digest = keccak256(
            abi.encodePacked(
                "\x19\x01",
                domainSeparator(),
                keccak256(
                    abi.encode(_PERMIT_TYPEHASH, owner, spender, amount, _nonces[owner]++, deadline)
                )
            )
        );
        address recoveredAddress = ecrecover(digest, v, r, s);
        require(recoveredAddress == owner, "EBTC: invalid signature");
        _approve(owner, spender, amount);
    }

An attacker can compute another corresponding [v,r,s] that will make this check pass due to the symmetrical nature of the elliptic curve. The easiest way to prevent this issue is to use OpenZeppelin’s ECDSA.sol library and reading the comments above ECDSA's tryRecover() function provides very useful information on correctly implementing signature checks to prevent signature malleability vulnerabilities.

When using OpenZeppelin's ECDSA library, special care must be taken to use version 4.7.3 or greater, since previous versions contained a signature malleability bug.

Tools Used

Vscode

Recommended Mitigation Steps

Use OpenZeppelin’s ECDSA.sol

Assessed type

Invalid Validation

[bytes032]

https://gist.github.com/GalloDaSballo/a0f9766bf7bac391f49d2d167e947de0#permit-signatures-are-malleable

Invalid

[c4-pre-sort]

bytes032 marked the issue as insufficient quality report

[c4-pre-sort]

bytes032 marked the issue as duplicate of #94

[c4-judge]

jhsagd76 marked the issue as unsatisfactory:
Out of scope