## Description The EVM side bridge implementation allows arbitrarily sized extra data to be included in deposits, while the SVM side forcibly truncates this data to 32 bytes. This protocol mismatch leads to silent data loss and can lead to unexpected protocol behavior. ## Impact - Silently drops data bytes beyond the first 32 bytes on the SVM side - Loss of transaction metadata or execution context - Potential failure of cross-chain applications relying on extra data On the EVM side, the **bridgeETHTo()** function accepts an extra data without any bounds: ```solidity function bridgeETHTo(bytes32 _to, uint32 _minGasLimit, bytes calldata _extraData) public payable { _initiateBridgeETH(msg.sender, _to, msg.value, _minGasLimit, _extraData); } ``` On the SVM side, ```rust impl TryFrom> for EthDepositData { type Error = DepositError; fn try_from(value: Vec) -> Result { // ... let mut extra_data = value[96..].to_vec(); extra_data.resize(32, 0); // Forces truncation to 32 bytes Ok(Self { from, to, amount, extra_data, }) } } ``` ## Proof of Concept Created a PoC by re-using existing tests and updating the **test_bridgeETHTo_succeeds** case in the `L1StandardBridge.t.sol` file. ```solidity function test_bridgeETHTo_succeeds() external { _preBridgeETHTo({ isLegacy: false, value: 6_000_000 gwei }); vm.recordLogs(); bytes memory extraData = bytes("this accepts a very large bytes string thats definitely of size more than 100 and its very concerning"); console.log(extraData.length, "length"); l1StandardBridge.bridgeETHTo{ value: 6_000_000 gwei }(alice_l2, 60000, bytes("this accepts a very large bytes string thats definitely of size more than 100 and its very concerning")); Vm.Log[] memory logs = vm.getRecordedLogs(); bytes32 sentMessageSelector = keccak256( "SentMessage(bytes32,address,bytes,uint256,uint256)" ); console.logBytes32(sentMessageSelector); console.log("------------------------"); for(uint256 i; i < logs.length; i++) { console.logBytes32(logs[i].topics[0]); if(logs[i].topics[0] == sentMessageSelector) { (address a, bytes memory b, ,) = abi.decode(logs[i].data, (address, bytes, uint256, uint256)); console.logBytes(b); a.call(b); } } assertEq(address(optimismPortal).balance, 6_000_000 gwei); } ``` In the above PoC, it can noted that we can send a byte of huge size without any limitation. ## Recommendation 1. Enforce size limit on the EVM side: ```solidity function bridgeETHTo(bytes32 _to, uint32 _minGasLimit, bytes calldata _extraData) public payable { require(_extraData.length <= 32, "Extra data exceeds 32 bytes"); _initiateBridgeETH(msg.sender, _to, msg.value, _minGasLimit, _extraData); } ``` 2. Support more extensive data on the SVM side: ```rust impl TryFrom> for EthDepositData { type Error = DepositError; fn try_from(value: Vec) -> Result { // ... let extra_data = value[96..].to_vec(); Ok(Self { from, to, amount, extra_data, // Keep full data }) } } ```

Sujith S

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