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Submission Details
Severity: medium
Invalid

abi.encodePacked Allows Hash Collision

kwakudr

Summary

abi.encodePacked results in Hash Collision sometimes when two dynamic arguments are encoded with it. From the https://docs.soliditylang.org/en/v0.8.17/abi-spec.html?highlight=collisions#non-standard-packed-mode:

If you use keccak256(abi.encodePacked(a, b)) and both a and b are dynamic types, it is easy to craft collisions in the hash value by moving parts of an into b and vice-versa. More specifically, abi.encodePacked("a", "bc") == abi.encodePacked("ab", "c").

Vulnerability Details

function quote(
uint32 _dstEid,
address _to,
uint256 _amount,
bytes memory _options
) external view returns (MessagingFee memory fee) {
return _quote(_dstEid, abi.encodePacked(_to, _amount), _options, false);
}
function teleport(
uint32 dstEid,
address to,
uint256 amount,
bytes calldata options
) external payable override returns(MessagingReceipt memory receipt) {
if (amount == 0) { revert CommonEventsAndErrors.ExpectedNonZero(); }
if (to == address(0)) { revert CommonEventsAndErrors.InvalidAddress(); }
// Encodes the message before invoking _lzSend.
bytes memory _payload = abi.encodePacked(to.addressToBytes32(), amount);
// debit
temple.burnFrom(msg.sender, amount);
emit TempleTeleported(dstEid, msg.sender, to, amount);
​
​
receipt = _lzSend(dstEid, _payload, options, MessagingFee(msg.value, 0), payable(msg.sender));
}

https://docs.soliditylang.org/en/v0.8.17/abi-spec.html?highlight=collisions#non-standard-packed-mode

As the solidity docs describe, two or more dynamic types are passed to abi.encodePacked. Moreover, these dynamic values are user-specified function arguments in external functions, meaning anyone can directly specify the value of these arguments when calling the function. Many users can fail an issue while claiming their prizes because of this.

Impact

  • Alice, a very deserving user, make a function call to claim their amount

  • But due to abi.encodePacked's hash collision verification fails

  • And Alice is unable to claim his prize.

Tools Used

Manual Review

Recommendations

Use abi.encode() instead of abi.encodePacked(), which will prevent hash collisions

Reference: https://github.com/sherlock-audit/2022-10-nftport-judging/issues/118

Updates

Lead Judging Commences

inallhonesty Lead Judge 11 months ago
Submission Judgement Published
Invalidated
Reason: Known issue

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