58192 sc high tokeautoeth strategy tokens locked when autopool router enforces maxdeposit cap

Submitted on Oct 31st 2025 at 09:43:06 UTC by @T0nraq for Audit Comp | Alchemix V3

• Report ID: #58192

• Report Type: Smart Contract

• Report severity: High

• Target: https://github.com/alchemix-finance/v3-poc/blob/immunefi_audit/src/strategies/mainnet/TokeAutoEth.sol

• Impacts:

  • Permanent freezing of funds

Description

Summary

The TokeAutoEth strategy's use of router.depositMax() causes WETH tokens to become permanently locked in the strategy contract when router::maxDeposit limits are enforced. The VaultV2 transfers the full requested amount to the strategy, but depositMax() only deposits min(balance, maxDeposit), leaving the difference trapped in the contract with no recovery mechanism.

Vulnerable Code

VaultV2 Transfers Full Amount to Strategy

File: lib/vault-v2/src/VaultV2.sol

function allocateInternal(address adapter, bytes memory data, uint256 assets) internal {
        require(isAdapter[adapter], ErrorsLib.NotAdapter());

        accrueInterest();

        SafeERC20Lib.safeTransfer(asset, adapter, assets); // <<<<<@ full amt sent
        (bytes32[] memory ids, int256 change) = IAdapter(adapter).allocate(data, assets, msg.sig, msg.sender);

        for (uint256 i; i < ids.length; i++) {
            Caps storage _caps = caps[ids[i]];
            _caps.allocation = (int256(_caps.allocation) + change).toUint256();

            require(_caps.absoluteCap > 0, ErrorsLib.ZeroAbsoluteCap());
            require(_caps.allocation <= _caps.absoluteCap, ErrorsLib.AbsoluteCapExceeded());
            require(
                _caps.relativeCap == WAD || _caps.allocation <= firstTotalAssets.mulDivDown(_caps.relativeCap, WAD),
                ErrorsLib.RelativeCapExceeded()
            );
        }
        emit EventsLib.Allocate(msg.sender, adapter, assets, ids, change);
    }

Strategy Allocation (Fails to Deploy Full Amount)

File: src/strategies/mainnet/TokeAutoEth.sol Lines: 56-63

function _allocate(uint256 amount) internal override returns (uint256) {
    require(TokenUtils.safeBalanceOf(address(weth), address(this)) >= amount, "Strategy balance is less than amount");
    
    // Approves full amount received from vault
    TokenUtils.safeApprove(address(weth), address(router), amount);
    
    // But depositMax() may deposit LESS than amount due to maxDeposit cap
    uint256 shares = router.depositMax(autoEth, address(this), 0);
    
    TokenUtils.safeApprove(address(autoEth), address(rewarder), shares);
    rewarder.stake(address(this), shares);
    
    // Returns amount, claiming full deployment even if partial
    return amount;
}

Router DepositMax (Caps at maxDeposit)

Contract: AutopilotRouter (0x37dD409f5e98aB4f151F4259Ea0CC13e97e8aE21)

function depositMax(
    IAutopool vault,
    address to,
    uint256 minSharesOut
) public payable override returns (uint256 sharesOut) {
    IERC20 asset = IERC20(vault.asset());
    uint256 assetBalance = asset.balanceOf(msg.sender);
    
    // Gets vault's maximum deposit limit
    uint256 maxDeposit = vault.maxDeposit(to);
    
    // Takes MINIMUM of balance and maxDeposit
    // If maxDeposit < balance, excess tokens are left behind
    uint256 amount = maxDeposit < assetBalance ? maxDeposit : assetBalance;
    
    pullToken(asset, amount, address(this));
    approve(IERC20(vault.asset()), address(vault), amount);
    return deposit(vault, to, amount, minSharesOut);
}

Vulnerability Details

The Token Lock Flow

Step 1: VaultV2 transfers full amount to strategy

// Allocator requests allocation of 1000 WETH
_allocate(tokeAutoEthStrategy, 1000e18);

// VaultV2 transfers ENTIRE 1000 WETH to strategy
IERC20(WETH).safeTransfer(tokeAutoEthStrategy, 1000e18);

Step 2: Strategy approves and calls depositMax

// Strategy has 1000 WETH balance
TokenUtils.safeApprove(address(weth), address(router), 1000e18); // Approves 1000 WETH

// Calls router.depositMax()
uint256 shares = router.depositMax(autoEth, address(this), 0);

Step 3: Router caps deposit at maxDeposit limit

// Router checks vault limits
uint256 assetBalance = asset.balanceOf(msg.sender);  // Returns 1000 WETH
uint256 maxDeposit = vault.maxDeposit(to);           // Returns 900 WETH (vault is near capacity)

// Takes MINIMUM - only deposits 900 WETH
uint256 amount = maxDeposit < assetBalance ? maxDeposit : assetBalance; // amount = 900 WETH

// Deposits only 900 WETH to vault
pullToken(asset, 900e18, address(this));

Step 4: Excess tokens are locked

// Strategy balance after deposit: 1000 - 900 = 100 WETH
// These 100 WETH are PERMANENTLY LOCKED:
// - No mechanism to return them to VaultV2
// - No recovery function exists
// - Cannot be reallocated or withdrawn

Root Cause Analysis

The vulnerability arises from a three-way contract interaction failure:

1. VaultV2 Assumption: Transfers full amount expecting complete deployment

2. Router Reality: Respects maxDeposit limits and may deposit less

3. Strategy Gap: No logic to handle partial deposits or return excess funds

The strategy's _allocate() function returns amount (claiming full deployment) even when only a portion was actually deposited, creating an accounting mismatch that traps the difference.

Impact

Severity Justification

• Permanent Capital Loss: Tokens become irrecoverably stuck in strategy

Recommended Fix

Direct Vault Deposit with Limit Enforcement (Recommended)

Replace router.depositMax() with direct vault deposit and enforce limits upfront:

function _allocate(uint256 amount) internal override returns (uint256) {
    require(TokenUtils.safeBalanceOf(address(weth), address(this)) >= amount, "Strategy balance is less than amount");
    
    // Check maxDeposit BEFORE attempting allocation
    uint256 maxDeposit = autoEth.maxDeposit(address(this));
    require(amount <= maxDeposit, "Amount exceeds vault deposit limit");
    
    // Approve and deposit exact amount
    TokenUtils.safeApprove(address(weth), address(autoEth), amount);
    uint256 shares = autoEth.deposit(amount, address(this));
    
    TokenUtils.safeApprove(address(autoEth), address(rewarder), shares);
    rewarder.stake(address(this), shares);
    return amount;
}

References

• POC Test: test/TokeAutoEthBugs.t.sol::test_TokenLockWhenMaxDepositExceeded

• Vulnerable Code: src/strategies/mainnet/TokeAutoEth.sol:66

• VaultV2 Transfer: lib/vault-v2/src/VaultV2.sol (allocate function)

• Router Contract: AutopilotRouter 0x37dD409f5e98aB4f151F4259Ea0CC13e97e8aE21

Proof of Concept

Proof of Concept

Steps to run POC

1. Create directory v3-poc/test/TokeAutoEthBugs.t.sol

2. Paste the snippet below in the newly created file and run with forge test

// SPDX-License-Identifier: MIT
pragma solidity 0.8.28;

import "forge-std/Test.sol";
import "forge-std/console.sol";

/**
 * @title TokeAutoEthBugsTest
 * @notice This test demonstrates two critical bugs in the TokeAutoEthStrategy._allocate() function
 * 
 * BUG 1: max balance deposit.
 * - router.depositMax() deposits the ENTIRE balance of msg.sender, not just the approved amount
 * - An attacker can frontrun and send 1 wei of WETH to the strategy contract
 * - This causes router to try depositing more than the approved amount, resulting in a revert
 * 
 * BUG 2: Token Lock/Loss
 * - If the strategy contract holds more WETH than vault.maxDeposit(to) allows
 * - router.depositMax() will only deposit up to maxDeposit amount
 * - The remaining WETH gets stuck in the strategy contract with no recovery mechanism
 */
contract TokeAutoEthBugsTest is Test {
    // Mock contracts
    MockWETH public weth;
    MockAutoEthVault public autoEth;
    MockAutopilotRouter public router;
    MockRewarder public rewarder;
    TokeAutoEthStrategyMock public strategy;
    
    address public attacker = address(0xBEEF);
    address public strategyOwner = address(0xABCD);
    
    function setUp() public {
        // Deploy mocks
        weth = new MockWETH();
        autoEth = new MockAutoEthVault(address(weth));
        rewarder = new MockRewarder();
        router = new MockAutopilotRouter(address(weth), address(autoEth));
        
        // Deploy strategy
        strategy = new TokeAutoEthStrategyMock(
            address(weth),
            address(autoEth),
            address(router),
            address(rewarder)
        );
        
        // Fund strategy with WETH for normal operation
        weth.mint(address(strategy), 100 ether);
    }
    
    /**
     * @notice BUG 1: Demonstrates frontrun DOS attack
     * @dev An attacker sends 1 wei of WETH to the strategy, causing allocation to fail
     */
    // function test_Bug1_maxBalanaceUsage() public {
    //     uint256 amountToAllocate = 10 ether;
        
    //     // Initial balance check
    //     uint256 initialBalance = weth.balanceOf(address(strategy));
    //     assertEq(initialBalance, 100 ether);
        
    //     // ATTACKER FRONTRUNS: Sends 1 wei of WETH to strategy
    //     vm.prank(attacker);
    //     weth.mint(address(strategy), 1);
        
    //     uint256 balanceAfterAttack = weth.balanceOf(address(strategy));
    //     assertEq(balanceAfterAttack, 100 ether + 1);
        
    //     // Now when strategy tries to allocate, it will fail
    //     // The strategy approves only 'amount' but router tries to deposit entire balance
    //     vm.expectRevert("ERC20: insufficient allowance");
    //     strategy.allocate(amountToAllocate);
        
    //     console.log("BUG 1 DEMONSTRATED:");
    //     console.log("- Strategy approved:", amountToAllocate);
    //     console.log("- Strategy balance:", balanceAfterAttack);
    //     console.log("- Router tried to deposit:", balanceAfterAttack);
    //     console.log("- Result: REVERT - Complete DOS");
    // }
    
    /**
     * @notice BUG 2: Demonstrates token lock when balance exceeds maxDeposit
     * @dev When strategy has more WETH than vault's maxDeposit, excess tokens get locked
     */
    function test_Bug2_TokenLock() public {
        // Set vault's maxDeposit to a lower amount
        uint256 maxDeposit = 50 ether;
        autoEth.setMaxDeposit(maxDeposit);
        
        uint256 amountToAllocate = 100 ether; // More than maxDeposit
        uint256 initialBalance = weth.balanceOf(address(strategy));
        
        assertEq(initialBalance, 100 ether);
        assertEq(autoEth.maxDeposit(address(strategy)), maxDeposit);
        
        // Strategy approves full amount and calls router.depositMax
        strategy.allocate(amountToAllocate);
        
        // Check what happened
        uint256 finalBalance = weth.balanceOf(address(strategy));
        uint256 deposited = initialBalance - finalBalance;
        uint256 locked = finalBalance;
        
        console.log("\nBUG 2 DEMONSTRATED:");
        console.log("- Initial balance:", initialBalance);
        console.log("- Approved amount:", amountToAllocate);
        console.log("- Max deposit allowed:", maxDeposit);
        console.log("- Actually deposited:", deposited);
        console.log("- Tokens LOCKED in contract:", locked);
        
        // Assert that tokens are locked
        assertEq(deposited, maxDeposit, "Only maxDeposit amount was deposited");
        assertEq(locked, 50 ether, "50 ether is now locked in the strategy");
        assertGt(locked, 0, "Tokens are stuck in strategy with no recovery");
    }
    

}

/**
 * @notice Simplified mock of TokeAutoEthStrategy to demonstrate bugs
 */
contract TokeAutoEthStrategyMock {
    address public immutable weth;
    address public immutable autoEth;
    MockAutopilotRouter public immutable router;
    address public immutable rewarder;
    
    constructor(
        address _weth,
        address _autoEth,
        address _router,
        address _rewarder
    ) {
        weth = _weth;
        autoEth = _autoEth;
        router = MockAutopilotRouter(_router);
        rewarder = _rewarder;
    }
    
    function allocate(uint256 amount) external returns (uint256) {
        require(MockWETH(weth).balanceOf(address(this)) >= amount, "Strategy balance is less than amount");
        
        // BUG: Only approves 'amount' but router will try to deposit ENTIRE balance
        MockWETH(weth).approve(address(router), amount);
        
        // This is where both bugs occur:
        // BUG 1: If balance > amount (due to frontrun), this reverts with insufficient allowance
        // BUG 2: If balance > maxDeposit, only maxDeposit is used, rest is locked
        uint256 shares = router.depositMax(MockAutoEthVault(autoEth), address(this), 0);
        
        MockAutoEthVault(autoEth).approve(address(rewarder), shares);
        MockRewarder(rewarder).stake(address(this), shares);
        
        return amount;
    }
}

/**
 * @notice Mock AutopilotRouter that mimics the real implementation
 */
contract MockAutopilotRouter {
    address public immutable weth;
    address public immutable vault;
    
    constructor(address _weth, address _vault) {
        weth = _weth;
        vault = _vault;
    }
    
    /**
     * @notice This is the actual depositMax implementation that causes the bugs
     * @dev It deposits min(msg.sender balance, maxDeposit) NOT the approved amount
     */
    function depositMax(
        MockAutoEthVault _vault,
        address to,
        uint256 minSharesOut
    ) external returns (uint256 sharesOut) {
        // BUG SOURCE: Uses msg.sender's ENTIRE balance, not approved amount
        uint256 assetBalance = MockWETH(weth).balanceOf(msg.sender);
        uint256 maxDeposit = _vault.maxDeposit(to);
        
        // BUG 2: If assetBalance > maxDeposit, only deposits maxDeposit
        uint256 amount = maxDeposit < assetBalance ? maxDeposit : assetBalance;
        
        // BUG 1: This will revert if amount > approved amount
        MockWETH(weth).transferFrom(msg.sender, address(_vault), amount);
        
        return _vault.deposit(amount, to);
    }
}

/**
 * @notice Mock WETH token
 */
contract MockWETH {
    string public name = "Wrapped Ether";
    string public symbol = "WETH";
    uint8 public decimals = 18;
    
    mapping(address => uint256) public balanceOf;
    mapping(address => mapping(address => uint256)) public allowance;
    
    function approve(address spender, uint256 amount) external returns (bool) {
        allowance[msg.sender][spender] = amount;
        return true;
    }
    
    function transfer(address to, uint256 amount) external returns (bool) {
        require(balanceOf[msg.sender] >= amount, "ERC20: insufficient balance");
        balanceOf[msg.sender] -= amount;
        balanceOf[to] += amount;
        return true;
    }
    
    function transferFrom(address from, address to, uint256 amount) external returns (bool) {
        require(balanceOf[from] >= amount, "ERC20: insufficient balance");
        require(allowance[from][msg.sender] >= amount, "ERC20: insufficient allowance");
        
        balanceOf[from] -= amount;
        balanceOf[to] += amount;
        allowance[from][msg.sender] -= amount;
        
        return true;
    }
    
    function mint(address to, uint256 amount) external {
        balanceOf[to] += amount;
    }
}

/**
 * @notice Mock AutoEth Vault (ERC4626)
 */
contract MockAutoEthVault {
    address public immutable asset;
    uint256 public totalAssets;
    uint256 public totalSupply;
    uint256 private _maxDeposit = type(uint256).max;
    
    mapping(address => uint256) public balanceOf;
    mapping(address => mapping(address => uint256)) public allowance;
    
    constructor(address _asset) {
        asset = _asset;
    }
    
    function maxDeposit(address) external view returns (uint256) {
        return _maxDeposit;
    }
    
    function setMaxDeposit(uint256 amount) external {
        _maxDeposit = amount;
    }
    
    function deposit(uint256 assets, address receiver) external returns (uint256 shares) {
        require(assets <= _maxDeposit, "Exceeds max deposit");
        
        totalAssets += assets;
        shares = assets; // 1:1 for simplicity
        totalSupply += shares;
        balanceOf[receiver] += shares;
        
        return shares;
    }
    
    function approve(address spender, uint256 amount) external returns (bool) {
        allowance[msg.sender][spender] = amount;
        return true;
    }
    
    function convertToShares(uint256 assets) external pure returns (uint256) {
        return assets; // 1:1 for simplicity
    }
    
    function convertToAssets(uint256 shares) external pure returns (uint256) {
        return shares; // 1:1 for simplicity
    }
}

/**
 * @notice Mock Rewarder
 */
contract MockRewarder {
    mapping(address => uint256) public balanceOf;
    
    function stake(address account, uint256 amount) external {
        balanceOf[account] += amount;
    }
    
    function withdraw(address account, uint256 amount, bool claim) external {
        require(balanceOf[account] >= amount, "Insufficient balance");
        balanceOf[account] -= amount;
    }
    
    function earned(address) external pure returns (uint256) {
        return 0;
    }
}