denial-of-service

Denial of Service

Unbounded Loops Over Dynamic Arrays

Iterating over arrays that grow with user interaction will eventually exceed the block gas limit.

// VULNERABLE: array grows unboundedly
address[] public stakers;

function distributeRewards() external {
    // If stakers.length > ~1500, this exceeds block gas limit
    for (uint256 i; i < stakers.length; ++i) {
        _sendReward(stakers[i]);
    }
}

Defense: Pull Pattern

// Users claim their own rewards — no unbounded iteration
mapping(address => uint256) public pendingRewards;

function claimReward() external {
    uint256 amount = pendingRewards[msg.sender];
    if (amount == 0) revert NothingToClaim();

    pendingRewards[msg.sender] = 0;

    (bool success,) = msg.sender.call{value: amount}("");
    if (!success) revert TransferFailed();

    emit RewardClaimed(msg.sender, amount);
}

Defense: Paginated Processing

uint256 public lastProcessedIndex;

function distributeRewards(uint256 batchSize) external {
    uint256 end = lastProcessedIndex + batchSize;
    if (end > stakers.length) end = stakers.length;

    for (uint256 i = lastProcessedIndex; i < end;) {
        _sendReward(stakers[i]);
        unchecked { ++i; }
    }

    lastProcessedIndex = end;

    if (end == stakers.length) {
        lastProcessedIndex = 0; // reset for next round
        emit DistributionComplete();
    }
}

External Call Failures Blocking Execution

A single failing external call in a loop blocks all subsequent operations.

// VULNERABLE: one failed transfer blocks all
function distributeAll(address[] calldata recipients, uint256[] calldata amounts) external {
    for (uint256 i; i < recipients.length; ++i) {
        IERC20(token).safeTransfer(recipients[i], amounts[i]); // if one reverts, all fail
    }
}

// FIXED: record failures, continue processing
function distributeAll(address[] calldata recipients, uint256[] calldata amounts) external {
    for (uint256 i; i < recipients.length;) {
        try IERC20(token).transfer(recipients[i], amounts[i]) returns (bool success) {
            if (!success) {
                pendingClaims[recipients[i]] += amounts[i];
                emit DistributionFailed(recipients[i], amounts[i]);
            }
        } catch {
            pendingClaims[recipients[i]] += amounts[i];
            emit DistributionFailed(recipients[i], amounts[i]);
        }
        unchecked { ++i; }
    }
}