RACE #27 Of The Secureum Bootcamp Epoch∞

This is a Write-Up of RACE-27, Quiz of the Secureum Bootcamp (opens in a new tab) for Ethereum Smart Contract Auditors. It was designed by the Secureum Mentor Alex The Entreprenerd (opens in a new tab), Security Researcher at Spearbit, Judge at Code4rena and former Smart Contract Developer at BadgerDAO.

Participants of this quiz had to answer 8 questions within the strict time limit of 16 minutes. If you’re reading this in preparation for participating yourself, it’s best to give it a try under the same time limit!

As usual, I waited for submissions to close before publishing it and, to stay true to the original, I omitted syntax highlighting. Feel free to copy it into your favorite editor, but do so after starting the timer!

March 4, 2024 by patrickd

Code

All 8 questions in this RACE are based on the code snippet below, which was shown for all questions.

// SPDX-License-Identifier: GPL-2.0
pragma solidity 0.8.20;

import "@[email protected]/contracts/utils/Multicall.sol";
import "@[email protected]/contracts/metatx/ERC2771Context.sol";
import "@[email protected]/contracts/security/ReentrancyGuard.sol";


interface IToken {
   function transfer(address, uint256) external returns (bool);
   function approve(address, uint256) external;

   function balanceOf(address) external view returns (uint256);
}


interface ISwapper {
   function swap(address tokenIn, address tokenOut, uint256 amountIn, uint256 amountOutMin) external;
}
interface IStrategy {
   function want() external view returns (address);
   function reward() external view returns (address);
}


contract Controller is Multicall, ERC2771Context {
   address immutable OWNER;

   mapping(address => bool) isStrategy;
   mapping(address => bool) isDivested;
   mapping(address => mapping(address => bool)) allowedSwap;
   mapping(address => uint256) lastSafeBalanceOfWant;

   constructor(address owner, address trustedForwarder_) ERC2771Context(trustedForwarder_) public {
       OWNER = owner;
   }

   modifier onlyOwner() {
       require(_msgSender() == OWNER, "onlyOwner");
       _;
   }

   function registerStrategy(address strategy) external onlyOwner returns (uint256) {
       address want = IStrategy(strategy).want();
       address reward = IStrategy(strategy).reward();
       require(!allowedSwap[reward][want], "Cannot add same swap route");


       allowedSwap[reward][want] = true;
       isStrategy[strategy] = true;
   }

   /** Multicallable Operations */
   function divest(address strategy, uint256 amt, uint256 minOut) external onlyOwner returns (uint256) {
       require(isStrategy[strategy], "Must be registered");
       require(!isDivested[strategy], "Must be Invested!");
       isDivested[strategy] = true;
       bool healthCheck = Strategy(strategy).shouldDivest();
       require(healthCheck, "Must be in emergency");
       Strategy(strategy).divest(amt, minOut);

       lastSafeBalanceOfWant[strategy] = IToken(Strategy(strategy).want()).balanceOf(strategy);
   }

   function invest(address strategy, uint256 minOut) external onlyOwner returns (uint256) {
       require(isDivested[strategy]);
       require(isStrategy[strategy], "Must be registered");
       IToken token = IToken(address(IStrategy(strategy).want()));
       uint256 amt = token.balanceOf(address(this));
       require(amt >= lastSafeBalanceOfWant[strategy]); // Ensure we didn't lose value on divest
       token.transfer(strategy, amt);
       Strategy(strategy).invest(amt, minOut);

       isDivested[strategy] = false;
   }

   function harvestSwap(ISwapper swapper, address tokenIn, address tokenOut, uint256 amountIn, uint256 amountOutMin, address strategy)
       external
       onlyOwner
       returns (uint256)
   {
       require(allowedSwap[tokenIn][tokenOut], "Must be allowed");
       IToken reward = IToken(address(IStrategy(strategy).reward()));
       IToken want = IToken(address(IStrategy(strategy).want()));

       require(address(reward) == tokenIn);
       require(address(want) == tokenOut);

       IToken(address(tokenIn)).approve(address(swapper), 0);
       IToken(address(tokenIn)).approve(address(swapper), amountIn);

       swapper.swap(tokenIn, tokenOut, amountIn, amountOutMin);
       want.transfer(strategy, want.balanceOf(address(this)));       
   }
}


interface ICurvePool {
   // Add with WETH
   function add_liquidity(uint256[] memory amounts, uint256 min_mint_amount) external;
   function remove_liquidity(uint256 _amount, uint256[] memory _min_amounts) external;
   function remove_liquidity_one_coin(uint256 token_amount, uint256 i, uint256 min_amount) external;
   function exchange(uint256 i, uint256 j, uint256 dx, uint256 min_dy, bool useETh) external;
   function balances(uint256) external view returns (uint256);

   function D() external returns (uint256);
   function virtual_price() external returns (uint256);
   function get_virtual_price() external returns (uint256);
  
   function totalSupply() external view returns (uint256);
}


interface IGauge {   
   function balanceOf(address) external view returns (uint256);
   function deposit(uint256) external;
   function withdraw(uint256) external;

   function claim_rewards() external;
}


contract Strategy is ReentrancyGuard {
   address public immutable CONTROLLER;
   address public immutable want;
   address public immutable reward;

   uint256 constant PRECISION = 1e18; // 50%
   uint256 constant IDLE_AMOUNT = 5; // 5%
   uint256 constant IDLE_PRECISION = 100; // 5%
  
   // https://arbiscan.io/address/0x82aF49447D8a07e3bd95BD0d56f35241523fBab1
   uint256 constant WETH_INDEX = 2;


   // https://arbiscan.io/address/0x960ea3e3C7FB317332d990873d354E18d7645590
   ICurvePool pool = ICurvePool(0x960ea3e3C7FB317332d990873d354E18d7645590);
   IGauge gauge = IGauge(0x555766f3da968ecBefa690Ffd49A2Ac02f47aa5f);

   constructor(address controller, address _want, address _reward) public {
       CONTROLLER = controller;
       want = _want;
       reward = _reward;

       IToken(_want).approve(address(pool), type(uint256).max);
       IToken(address(pool)).approve(address(gauge), type(uint256).max);
   }

   modifier onlyController() {
       require(msg.sender == CONTROLLER);
       _;
   }

   function idleBalance() public view returns (uint256) {
       return IToken(want).balanceOf(address(this));
   }

   function balanceInPool() public view returns (uint256) {
       return IToken(address(gauge)).balanceOf(address(this));
   }
   function balanceOfRewards() public view returns (uint256) {
       return IToken(reward).balanceOf(address(this));
   }

   // Get Total Value we would have if we withdrew WETH
   function investedBalance() external view returns (uint256) {
       uint128 bal_1 = uint128(pool.balances(WETH_INDEX));
       uint256 calculatedBalance = bal_1 * PRECISION * balanceInPool() / pool.totalSupply() / PRECISION;

       return calculatedBalance;
   }

   // We should divest when something goes wrong, avoids bricking the pool
   function shouldDivest() external view returns (bool) {
       try this.investedBalance() {
           return false;
       } catch {
           return true; // Divest if something goes wrong
       }
      
       return false;
   }

   function invest(uint256 amt, uint256 minMint) external nonReentrant onlyController returns (uint256) {
       uint256 toKeep = idleBalance() * IDLE_AMOUNT / IDLE_PRECISION;
       uint256 toDeposit = idleBalance() - toKeep;

       uint256[] memory amounts = new uint256[](3);
       amounts[WETH_INDEX] = toDeposit;

       uint256 initialBal = balanceInPool();
       pool.add_liquidity(amounts, minMint);
       uint256 afterBal = balanceInPool();
       gauge.deposit(afterBal - initialBal);
   }

   function divest(uint256 amt, uint256 minOut) external nonReentrant onlyController returns (uint256) {
       gauge.withdraw(amt);
       uint256 initialBal = idleBalance();
       pool.remove_liquidity_one_coin(amt, WETH_INDEX, minOut);
       uint256 afterBal = idleBalance();
       IToken(reward).transfer(address(CONTROLLER), afterBal - initialBal);
   }

   function harvest() external nonReentrant {
       // Increases
       uint256 prevBalRewards = balanceOfRewards();
       gauge.claim_rewards();
       uint256 afterBalReward = balanceOfRewards();
       IToken(reward).transfer(address(CONTROLLER), afterBalReward - prevBalRewards);
   }
}

Question 1 of 8

Functions depositing and withdrawing from the Gauge:

A. Should use a reentrancy guard
B. Should have a minOut parameter
C. Should verify that we have sufficient balance before making the call
D. Are perfectly safe because it's an official Curve gauge

Solution

Correct is D.

A: The invest() and divest() functions, which are the only ones depositing or withdrawing from the gauge, are already using a reentrancy guard thanks to the nonReentrant modifier. This option implies that such a guard was missing, which is incorrect and makes this option false.

B: The divest() function already has such a parameter, for the invest() function its called minMint instead. Again both already have it, while the option implies that its missing. It can furthermore be noted that gauge contracts have no slippage, so these parameters aren't actually related to the fact that the gauge is being called.

C: Since the gauge does not want to get scammed, it'll check whether we have sufficient balance for us and there's no need to check this before making the call. If we had insufficient balance it would revert.

D: The gauge used is hardcoded and is indeed an official Curve gauge which will behave as expected by this code.

Question 2 of 8

The function shouldDivest:

A. Can never return true as the investedBalance function will not revert
B. Can revert because this may be selfdestructed when we delegatecall to a proxy
C. Can never return true because the catch clause doesn't catch Bytes Error
D. None of the above

Solution

Correct is D.

A: The investedBalance() function will revert when the uint256 value returned by balanceInPool() is too large to fit into uint128 when multiplied in bal_1 * PRECISION * balanceInPool(). This is because the expression is casted to uint128 because of bal_1, the fact that it is back-cast to uint256 in the end does not matter.

B: Random gibberish option.

C: The } catch { will catch all errors, even if it is some "Bytes Error", because it's not specifying anything specific that it is trying to catch.

Question 3 of 8

The owner can:

A. Steal all funds by withdrawing them to a malicious strategy
B. Lose their private key
C. Be impersonated due to Multicall and Meta Transactions support
D. Set only one strategy per reward and want combination

Solution

Correct is A, B, C.

A: The owner is capable of arbitrarily adding new strategies, and using invest() and divest() to move funds between them. A malicious owner could indeed simply add a strategy that allows stealing all of the funds after moving them there.

B: Protocol owners can indeed lose their private key, a simple and true statement. Sadly it happens all the time, or is used to cover up a rug pull. Since this is off-chain operational security, it's hard to tell and often not much thought is put into preventing it.

C: Account Impersonation is indeed possible through combining ERC-2771 and Multicall with the used version of OpenZeppelin which does not contain the appropriate fix yet. If you're unfamiliar with this bug, take a look at the detailed write-up about it (opens in a new tab) in the Ethereum Smart Contract Auditor's 2023 Rewind.

D: While there's code that prevents adding the same swap route in allowedSwap, this check is directional. Even if [reward][want] has already been set, there's always a second combination involving both of these values that is still allowed (basically [want][reward]).

Question 4 of 8

The System is:

A. Using a swapper to allow custom swaps in the future
B. A Template system for generating NFTs
C. Using a Controller and a Strategy where the Controller can work with only one strategy
D. None of the above

Solution

Correct is A.

A: It indeed appears to be using a "swapper".

B: Just random gibberish again.

C: The controller appears to work with many Strategies.

Question 5 of 8

The Strategy:

A. Cannot be forced to invest and divest due to ownership checks in the Controller
B. Can be made to lose all of its rewards by claiming on behalf of the strategy
C. Can be made to lose all of its rewards because the reward token is Fee-on-Transfer
D. Can send tokens to the wrong address

Solution

Correct is A, B.

A: These operations are indeed permissioned by an ownership check.

B: Is true when exploiting a gauge loss-of-yield attack (opens in a new tab).

C/D: More gibberish.

Question 6 of 8

Harvest for the Strategy:

A. Will claim reward tokens and send them to the Controller
B. Doesn't use safeTransfer and so it will revert
C. transfer will not revert because the reward token is known
D. Can overflow via a donation during gauge execution that requires no changes in the external contracts

Solution

Correct is A, C.

A: That's indeed what the code appears to do.

B/C: The token we're calling transfer() on is a hardcoded Curve token that is known to work as expected by this code. A safeTransfer wrapper would only be necessary if it's unknown how the used token handles errors.

D: You guessed it, gibberish it is.

Question 7 of 8

The mapping lastSafeBalanceOfWant[strategy]:

A. Is always zero
B. Should be zero if no direct donation has happened
C. Will track the balance of want of the controller
D. Will prevent sweep exploits in invest

Solution

Correct is B.

As you can tell from the code comment, the way that lastSafeBalanceOfWant[strategy] is currently used is incorrect and should be swapped.

A/B: Although it is most likely to be zero indeed, it can't be said that it's always zero because there's the possibility that a "direct donation" (ie. a injection of funds) happened.

C: It's not tracking as intended since setting the mapping's value and checking it are swapped.

D: Incorrect, this offers no protection.

Question 8 of 8

The function invest:

A. Allows the owner to deposit want, convert it into Tricrypto LP and stake in the gauge
B. Allows an attacker to deposit in the wrong strategy
C. Allows an attacker to cause loss of value because lastSafeBalanceOfWant[strategy] is ineffective
D. None of the above

Solution

Correct is A, B, C.

A: That's factually what it does. You can see that it's indeed "Tricrypto LP" by checking the gauge's token tracker in arbiscan (opens in a new tab).

B/C: Both are possible thanks to the ERC-2771 + Multicall bug mentioned in Question 3

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