Stratax Contracts
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Submission Details
Impact: medium
Likelihood: medium

Precision Loss From Integer Division in Stratax::calculateUnwindParams May Under/Overestimate Collateral Withdrawal

Author Revealed upon completion

Precision Loss From Integer Division in Stratax::calculateUnwindParams May Under/Overestimate Collateral Withdrawal

Description:
The function computes collateralToWithdraw using integer division:

function calculateUnwindParams(address _collateralToken, address _borrowToken)
public
view
returns (uint256 collateralToWithdraw, uint256 debtAmount)
{
...
@> collateralToWithdraw = (debtTokenPrice * debtAmount * 10 ** IERC20(_collateralToken).decimals())
/ (collateralTokenPrice * 10 ** IERC20(_borrowToken).decimals());
​
// Account for 5% slippage in swap
@> collateralToWithdraw = (collateralToWithdraw * 1050) / 1000;
​
return (collateralToWithdraw, debtAmount);
}
​

Solidity division truncates, so this calculation can lose precision and systematically round down. Since this value is then adjusted by a slippage buffer:

collateralToWithdraw = (collateralToWithdraw * 1050) / 1000;
​

any earlier truncation still affects the final result. With different token decimals (e.g., 6 vs 18) and price feeds with 8 decimals, rounding error can become material.

Impact:
Medium. Incorrect estimation of collateral to withdraw can lead to:

  • Withdrawing too little collateral → swap yields insufficient borrow token → unwind flow reverts or fails to fully repay debt.

  • Withdrawing too much collateral → unnecessarily reduces remaining collateral / worsens position outcomes.

Recommended Mitigation:
Use a full-precision mulDiv approach to reduce truncation and control rounding direction (often round up is safer here to ensure enough collateral is withdrawn).

+ import {Math} from "@openzeppelin/contracts/utils/math/Math.sol";
​
collateralToWithdraw =
- (debtTokenPrice * debtAmount * 10 ** IERC20(_collateralToken).decimals())
- / (collateralTokenPrice * 10 ** IERC20(_borrowToken).decimals());
+ Math.mulDiv(
+ debtTokenPrice * debtAmount,
+ 10 ** IERC20(_collateralToken).decimals(),
+ collateralTokenPrice * (10 ** IERC20(_borrowToken).decimals()),
+ Math.Rounding.Ceil
+ );
​

This minimizes precision loss and makes unwind calculations more reliable across token decimal configurations.

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