081.md

Powerful Honeysuckle Anteater

Medium

Borrowers which withdraw can be frontrun and the ODOS data could be used.

Summary

When doing a Borrower withdraw we perform signature verification in CDS.sol in verify() and we pass the ODOS data, which is later submitted to the ODOS router.

Root Cause

Reference CDS.sol#L878-L916

    function _verify(FunctionName functionName, uint256 excessProfitCumulativeValue, uint256 nonce,  bytes memory odosExecutionData,  bytes memory signature) private view returns (bool) {
        bytes32 digest;
        if (functionName == FunctionName.CDS_WITHDRAW) {
            digest = _hashTypedDataV4(
                keccak256(
                    abi.encode(
                        keccak256(
                            "Permit(uint256 excessProfitCumulativeValue,uint256 nonce)"
                        ),
                        excessProfitCumulativeValue,
                        nonce
                    )
                )
            );
 @>>     } else if (functionName == FunctionName.BORROW_WITHDRAW) {
            digest = _hashTypedDataV4(
@>>            keccak256(abi.encode(keccak256("OdosPermit(bytes odosExecutionData)"), odosExecutionData))
            );
        }

        address signer = ECDSA.recover(digest, signature);
        bytes32 hashedSigner = keccak256(abi.encodePacked(signer));
 @>>     if (hashedSigner == hashedAdminTwo) {
            return true;
        } else {
            return false;
        }
    }

https://optimistic.etherscan.io/address/0xca423977156bb05b13a2ba3b76bc5419e2fe9680#code - this is the odos contract.

Odos permits are handled here.

  function swapPermit2(
    permit2Info memory permit2,
    swapTokenInfo memory tokenInfo,
    bytes calldata pathDefinition,
    address executor,
    uint32 referralCode
  )
    external
    returns (uint256 amountOut)
  {
    ISignatureTransfer(permit2.contractAddress).permitTransferFrom(
@>>   ISignatureTransfer.PermitTransferFrom(
        ISignatureTransfer.TokenPermissions(
          tokenInfo.inputToken,
          tokenInfo.inputAmount
        ),
        permit2.nonce,
        permit2.deadline
      ),
      ISignatureTransfer.SignatureTransferDetails(
        tokenInfo.inputReceiver,
        tokenInfo.inputAmount
      ),
      msg.sender,
      permit2.signature
    );
    return _swap(
      tokenInfo,
      pathDefinition,
      executor,
      referralCode
    );
  }

ODOS makes sure that nonces cannot be reused, however this opens the possibility for someone to frontrun a withdraw of a user and use their ODOS data.

Attack Path

• User A (borrower) submits a transaction to withdraw his position
• User B frontruns User A and withdraws another position using User A's odosAssembledData

Impact

This would result in a Dos of User A.

Mitigation

No Response