Submission Details
Impact:
Likelihood:
Fee Calculation Precision Loss
Description
The fee calculation mechanism uses integer division which causes precision loss for small swap amounts, potentially allowing fee avoidance through micro-transactions and undermining the protocol's revenue model.
if (isReFiBuy) {
fee = buyFee;
emit ReFiBought(sender, swapAmount);
} else {
fee = sellFee;
@> uint256 feeAmount = (swapAmount * sellFee) / 100000;
emit ReFiSold(sender, swapAmount, feeAmount);
}
Risk
Impact:
-
Very small swaps may incur zero fees
-
Potential for fee avoidance through micro-transactions
-
Minor economic impact
Proof of Concept
Add the following to `RebateFiHookTest.t.sol`
function test_FeeCalculationPrecisionLoss() public {
uint256 smallSwapAmount = 100; // 100 wei
uint256 expectedFee = (smallSwapAmount * 3000) / 100000; // = 3 wei
uint256 tinySwapAmount = 1;
uint256 tinyFee = (tinySwapAmount * 3000) / 100000; // = 0 due to integer division
assertEq(tinyFee, 0); // Fee rounds down to 0
}
Recommended Mitigation
if (isReFiBuy) {
fee = buyFee;
- emit ReFiBought(sender, swapAmount);
+ uint256 feeAmount = (swapAmount * buyFee * SCALING_FACTOR) / 100000 / SCALING_FACTOR;
+ if (feeAmount == 0 && swapAmount > 0) feeAmount = MIN_FEE_AMOUNT;
+ emit ReFiBought(sender, swapAmount, feeAmount);
} else {
fee = sellFee;
- uint256 feeAmount = (swapAmount * sellFee) / 100000;
- emit ReFiSold(sender, swapAmount, feeAmount);
+ uint256 feeAmount = (swapAmount * sellFee * SCALING_FACTOR) / 100000 / SCALING_FACTOR;
+ if (feeAmount == 0 && swapAmount > 0) feeAmount = MIN_FEE_AMOUNT;
+ emit ReFiSold(sender, swapAmount, feeAmount);
}
Also:
-
Consider minimum swap amounts
-
Use scaled fee calculations for better precision
-
Accept as known limitation of integer math
Rewards breakdown
nSLOC
150This contest has a flat reward structure with the following payouts:
100 EXP
20 EXP
2 EXP
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