Lines of code

Vulnerability details

Impact

First depositor of the pool can break minting of the Bath Token shares

Proof of Concept

• An attacker -who is the first one to deposit- sends 1 wei and bypasses (totalSupply == 0) condition.

• Later a very large amount of donation to the pool and inflates the shares proportionality ratio.

• Subsequent depositors instead have to deposit an equivalent sum to avoid minting 0 shares. Otherwise, their deposits accrue to the attacker who holds the only share.

  function _deposit(uint256 assets, address receiver)
      internal
      returns (uint256 shares)
  {
      uint256 _pool = underlyingBalance();
      uint256 _before = underlyingToken.balanceOf(address(this));
  
  
      // **Assume caller is depositor**
      underlyingToken.transferFrom(msg.sender, address(this), assets);
      uint256 _after = underlyingToken.balanceOf(address(this));
      assets = _after.sub(_before); // Additional check for deflationary tokens
  
  
      (totalSupply == 0) ? shares = assets : shares = (
          assets.mul(totalSupply)
      ).div(_pool);
  
  
      // Send shares to designated target
      _mint(receiver, shares);
      emit LogDeposit(
          assets,
          underlyingToken,
          shares,
          msg.sender,
          underlyingBalance(),
          outstandingAmount,
          totalSupply
      );
      emit Deposit(msg.sender, msg.sender, assets, shares);
  }
  

<https://github.com/code-423n4/2022-05-rubicon/blob/8c312a63a91193c6a192a9aab44ff980fbfd7741/contracts/rubiconPools/BathToken.sol#L557-L585&gt;

Tools Used

Manual Review

Recommended Mitigation Steps

Ensure the number of shares to be minted is non-zero
Uniswap V2 solved this problem by sending the first 1000 LP tokens to the zero address. The same can be done in this case i.e. when totalSupply() == 0, send the first min liquidity LP tokens to the zero address to enable share dilution.

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