Submission Details
Severity:
User can liquidate himself to gain rewards
Summary
It seems that user can liquidate himself to gain reward.
Vulnerability Details
Impact
function liquidate(address collateral, address user, uint256 debtToCover)
external
moreThanZero(debtToCover)
nonReentrant
{
// need to check health factor of the user
uint256 startingUserHealthFactor = _healthFactor(user);
if (startingUserHealthFactor >= MIN_HEALTH_FACTOR) {
revert DSCEngine__HealthFactorOk();
}
// We want to burn their DSC "debt"
// And take their collateral
// Bad User: $140 ETH, $100 DSC
// debtToCover = $100
// $100 of DSC == ??? ETH?
// 0.05 ETH
uint256 tokenAmountFromDebtCovered = getTokenAmountFromUsd(collateral, debtToCover);
// And give them a 10% bonus
// So we are giving the liquidator $110 of WETH for 100 DSC
// We should implement a feature to liquidate in the event the protocol is insolvent
// And sweep extra amounts into a treasury
// 0.05 * 0.1 = 0.005. Getting 0.055
uint256 bonusCollateral = (tokenAmountFromDebtCovered * LIQUIDATION_BONUS) / LIQUIDATION_PRECISION;
uint256 totalCollateralToRedeem = tokenAmountFromDebtCovered + bonusCollateral;
_redeemCollateral(user, msg.sender, collateral, totalCollateralToRedeem);
// We need to burn the DSC
_burnDsc(debtToCover, user, msg.sender);
uint256 endingUserHealthFactor = _healthFactor(user);
if (endingUserHealthFactor <= startingUserHealthFactor) {
revert DSCEngine__HealthFactorNotImproved();
}
In function liquidate,there is no limitation weather borrower is liquidater himself.
Take a look at function redeem,which is to repay the borrow money.
function redeemCollateral(address tokenCollateralAddress, uint256 amountCollateral)
public
moreThanZero(amountCollateral)
nonReentrant
{
_redeemCollateral(msg.sender, msg.sender, tokenCollateralAddress, amountCollateral);
_revertIfHealthFactorIsBroken(msg.sender);
}
compare to liquidation logic
uint256 bonusCollateral = (tokenAmountFromDebtCovered * LIQUIDATION_BONUS) / LIQUIDATION_PRECISION;
uint256 totalCollateralToRedeem = tokenAmountFromDebtCovered + bonusCollateral;
user will get more collateral compare to repay .
Tools Used
manual
Recommendations
add limitation,liquidator can not be borrower
Prize pool breakdown
Total prize
15,000 USDC
nSLOC
23664 USDC / LOC
14,000 USDC
1,000 USDC
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