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Submission Details
Severity: medium
Invalid

Due to lack of subtraction of the `fee`, `s.vault[vault].zethTotal` would be misaccounted

0xmuxyz

Summary

Within the LibVault#removeZeth(), the fee would not be subtracted from the s.vault[vault].zethTotal.
This lead to misaccounting of the s.vault[vault].zethTotal.

Vulnerability Details

When a user withdraw their LST (stETH or rETH), the user call the BridgeRouterFacet#withdraw(). At that time, the user have to pay the withdrawal fee.

Within the BridgeRouterFacet#withdraw(), the LibVault#removeZeth() would be called with the fee like this:
https://github.com/Cyfrin/2023-09-ditto/blob/main/contracts/facets/BridgeRouterFacet.sol#L111

function withdraw(address bridge, uint88 zethAmount)
external
nonReentrant
onlyValidBridge(bridge)
{
if (zethAmount == 0) revert Errors.ParameterIsZero();
​
uint88 fee;
uint256 withdrawalFee = bridge.withdrawalFee();
uint256 vault;
if (bridge == rethBridge || bridge == stethBridge) {
vault = Vault.CARBON;
} else {
vault = s.bridge[bridge].vault;
}
​
if (withdrawalFee > 0) {
fee = zethAmount.mulU88(withdrawalFee);
zethAmount -= fee;
s.vaultUser[vault][address(this)].ethEscrowed += fee;
}
​
uint88 ethAmount = _ethConversion(vault, zethAmount);
vault.removeZeth(zethAmount, fee); ///<-------------------------- @audit
IBridge(bridge).withdraw(msg.sender, ethAmount);

Within the LibVault#removeZeth(),

  • amount + fee would be subtracted from the s.vaultUser[vault][msg.sender].ethEscrowed

  • amount would be subtracted from the s.vault[vault].zethTotal
    https://github.com/Cyfrin/2023-09-ditto/blob/main/contracts/libraries/LibVault.sol#L28-L29

function removeZeth(uint256 vault, uint88 amount, uint88 fee) internal {
AppStorage storage s = appStorage();
s.vaultUser[vault][msg.sender].ethEscrowed -= (amount + fee); ///<----------------- @audit
s.vault[vault].zethTotal -= amount; ///<----------------- @audit
}

However, within the LibVault#removeZeth() above, the fee would not be subtracted from the s.vault[vault].zethTotal.
This lead to misaccounting of the s.vault[vault].zethTotal.

Impact

Due to lack of subtraction of the fee, s.vault[vault].zethTotal would be misaccounted.

Tools Used

  • Foundry

Recommendations

Within the LibVault#removeZeth(), consider subtracting amount + fee from the s.vault[vault].zethTotal like this:

function removeZeth(uint256 vault, uint88 amount, uint88 fee) internal {
AppStorage storage s = appStorage();
s.vaultUser[vault][msg.sender].ethEscrowed -= (amount + fee);
+ s.vault[vault].zethTotal -= amount + fee;
- s.vault[vault].zethTotal -= amount;
}
Updates

Lead Judging Commences

0xnevi Lead Judge
about 2 years ago
0xnevi Lead Judge about 2 years ago
Submission Judgement Published
Invalidated
Reason: Other

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