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C4 Alchemix finding: Alchemist can mint AlTokens above their assigned ceiling by calling lowerHasMinted()

Judge decision: Med severity, picked to be included in final report #1

C4 finding submitted: (risk = 2 (Med Risk))

Wed, May 18, 1:03 PM

Lines of code

https://github.com/code-423n4/2022-05-alchemix/blob/de65c34c7b6e4e94662bf508e214dcbf327984f4/contracts-full/AlchemicTokenV2Base.sol#L111-L124 https://github.com/code-423n4/2022-05-alchemix/blob/de65c34c7b6e4e94662bf508e214dcbf327984f4/contracts-full/AlchemicTokenV2Base.sol#L189-L191

Vulnerability details

Impact

An alchemist / user can mint more than their alloted amount of AlTokens by calling lowerHasMinted() before they reach their minting cap.

Proof of Concept

Function mint() in AlchemicTokenV2Base.sol

function mint(address recipient, uint256 amount) external onlyWhitelisted {
  if (paused[msg.sender]) {
    revert IllegalState();
  }

  uint256 total = amount + totalMinted[msg.sender];
  if (total > mintCeiling[msg.sender]) {
    revert IllegalState();
  }

  totalMinted[msg.sender] = total;

  _mint(recipient, amount);
}

Note the require conditional check that total > mintCeiling[msg.sender].

In the same contract, there is the function lowerHasMinted() with the same permission level as mint and is thus callable by the same user as well.

function lowerHasMinted(uint256 amount) external onlyWhitelisted {
  totalMinted[msg.sender] = totalMinted[msg.sender] - amount;
}

It is clear that a user can accumulate an infinite (within supply) amount of AlTokens by calling lowerHasMinted() before any action that would make them exceed their minting cap.

Tools Used

Manual review, VScode

Recommended Mitigation Steps

Change the permissioning on lowerHasMinted() to be restricted to a higher permissioned role like onlySentinel() , or deprecate this function as I could not find any uses of it throughout the codebase or in tests.

QA report

Relevant portions of code are marked with @audit tag.

Low-01 Check return boolean value of call in gALCX.sol:reApprove()

  function reApprove() public {
      // @audit check success return value for approve
      bool success = alcx.approve(address(pools), type(uint256).max);
  }

Suggested: require(success, "failed to approve");

Low-02 Potential rug vector for malicious admins in EthAssetManager.sol:sweepToken()

  function sweepToken(address token, uint256 amount) external lock onlyAdmin {
      // @audit prevent withdraw of specific tokens like `curveToken`
      SafeERC20.safeTransfer(address(token), msg.sender, amount);
      emit SweepToken(token, amount);
  }

The functionality of sweepToken is used to send any amount of any ERC20 token held by the EthAssetManager to the admin. However, there is no restriction on which tokens can be sent. Thus, the admin, which can be an EOA address, can sweep all underlying curveTokens to themselves, stealing the rewards generated in Convex from the rewardReceiver (called by claimRewards()).

Same issue is in ThreePoolAssetManager.sol.

Recommended Mitigation Steps: Do not allow sweeping of the curveToken and/or any other critical tokens.

QA-01: Move gALCX.sol:reApprove() a line under to public functions section

  // @audit move to section below
  function reApprove() public {
      bool success = alcx.approve(address(pools), type(uint256).max);
  }

  // PUBLIC FUNCTIONS

QA-02: Emit event in TransmuterV2.sol:setCollateralSource()

function setCollateralSource(address _newCollateralSource) external {
  _onlyAdmin();
  buffer = _newCollateralSource;
  // @audit QA - emit NewCollateralSource event here
}

Events are often emitted for changes to state throughout the codebase,and a changing of the collateral source should warrant one too.