Alchemix Transmuter
Alchemix
DeFiFoundrySolidity
16,653 OP
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Submission Details
Severity: low
Invalid

Mutable State Variables that Should be Immutable

sauronsol

Summary

Several state variables in the contracts that are only set once during initialization are not marked as immutable, leading to unnecessary gas costs and potential security risks.

Vulnerability Details

From the test results:

function testGasComparison() public {
// Test non-immutable version
uint256 gasBefore = gasleft();
uint256 value1 = nonImmutable.doSomethingWithRoutes();
uint256 gasAfter = gasleft();
uint256 gasUsedNonImmutable = gasBefore - gasAfter;
// Test immutable version
gasBefore = gasleft();
uint256 value2 = immutable_.doSomethingWithRoutes();
gasAfter = gasleft();
uint256 gasUsedImmutable = gasBefore - gasAfter;
emit log_named_uint("Gas used non-immutable", gasUsedNonImmutable);
emit log_named_uint("Gas used immutable", gasUsedImmutable);
assertTrue(gasUsedImmutable < gasUsedNonImmutable, "Immutable should use less gas");
assertEq(value1, value2, "Values should be equal");
}
​
function testNonImmutableCanBeModified() public {
// Initial value
assertEq(nonImmutable.nRoutes(), 5);
// Can modify non-immutable
nonImmutable.setRoutes(10);
// Value changed
assertEq(nonImmutable.nRoutes(), 10, "Non-immutable value should be modifiable");
}
Gas used non-immutable: 7368
Gas used immutable: 5169

This shows a difference of ~2200 gas per read operation when using non-immutable vs immutable variables.

Affected variables include:

// In StrategyArb.sol
ITransmuter public transmuter; // Should be immutable
ERC20 public underlying; // Should be immutable
​
// In TokenAdapterMock.sol
address public token; // Should be immutable

Impact

Low/Gas Optimization

  1. Gas inefficiency: ~2200 gas wasted per read operation

  2. Risk potential: Non-immutable variables could theoretically be modified if setter functions are added later

  3. Test proves higher gas costs: 7368 vs 5169 gas (42% more expensive)

Tools Used

  • Slither static analyzer

  • Custom test suite (ImmutableRoutesTest)

  • Manual review

  • Foundry gas reporting

Recommendations

  1. Mark variables as immutable when they're only set in constructor:

ITransmuter public immutable transmuter;
ERC20 public immutable underlying;
address public immutable token;

  1. Benefits:

  • Gas savings of ~2200 gas per read

  • Clearer code intent

  • Elimination of potential future modification risks

  • Better compiler optimizations

Updates

Appeal created

inallhonesty Lead Judge 10 months ago
Submission Judgement Published
Invalidated
Reason: Non-acceptable severity
inallhonesty Lead Judge 10 months ago
Submission Judgement Published
Invalidated
Reason: Non-acceptable severity

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