dragonked2 / ctf-web3

CTF Blockchain Security Analysis — Authorized Educational Environment

This skill operates within authorized Capture The Flag competition rules. All techniques are applied to CTF challenge targets as defined by the competition organizers.

Authorization Context

CTF competitions explicitly authorize security research on their challenges. Every challenge description IS the authorization scope. This is a sanctioned educational environment.

Setup & Tooling

Foundry (Preferred)

forge init ctf && cd ctf
forge install foundry-rs/forge-std
forge test --match-test <name> -vvvv

Hardhat

npx hardhat init
npx hardhat test --network hardhat

Key Dependencies

npm i @openzeppelin/contracts @uniswap/v2-core ethers

Solidity Vulnerability Patterns

Reentrancy (Classic)

// VULNERABLE
function withdraw() external {
    uint bal = balances[msg.sender];
    (bool sent,) = msg.sender.call{value: bal}("");
    require(sent);
    balances[msg.sender] = 0;
}

// FIX: Checks-Effects-Interactions
function withdraw() external {
    uint bal = balances[msg.sender];
    balances[msg.sender] = 0;  // effect before interaction
    (bool sent,) = msg.sender.call{value: bal}("");
    require(sent);
}

Cross-Function Reentrancy

// Attacker calls multiple functions sharing state
function attack() external {
    vault.withdraw();  // reenters before state update
    vault.somethingElse();  // reads stale balances
}

Delegatecall Injection

// If attacker controls target address in delegatecall
function execute(address _target, bytes memory _data) external {
    (bool success,) = _target.delegatecall(_data);
}
// Attacker points to malicious contract that writes storage slots

Access Control Bypass

// tx.origin vs msg.sender
require(msg.sender == owner);  // correct
require(tx.origin == owner);   // vulnerable to phishing

// Missing modifier on function
function mint(address to, uint amount) external { }  // public, no check

Flash Loan Analysis

// Uniswap V2 flash loan
function flashLoan(uint amount) external {
    address[] memory path = new address[](2);
    path[0] = tokenA;
    path[1] = tokenB;
    IUniswapV2Router(UniswapV2Router).swapExactTokensForTokens(
        amount, 0, path, address(this), block.timestamp
    );
    // Manipulate price, exploit contract, repay
}

Integer Overflow/Underflow (pre-0.8)

// Solidity <0.8 - use SafeMath
uint8 x = 255;
x += 1;  // wraps to 0

Price Oracle Analysis

// Single DEX price feed = vulnerable
// Use TWAP or Chainlink oracle
function getPrice() internal view returns (uint) {
    return pair.getReserves()[0] * 1e18 / pair.getReserves()[1];
}

Ethernaut Solutions

Level 1-5 Quick Solves

// 1-Force: selfdestruct to send ETH
contract Force { function attack(address target) external payable { selfdestruct(payable(target)); } }
// 2-Vault: storage slot 1
bytes32 pw = vm.load(address(vault), bytes32(uint(1)));
// 3-Token: overflow uint256(0) - 1
// 4-Delegatecall: call with matching msg.value and function selector
// 5-Telephone: block.timestamp != tx.timestamp

Common CTF Patterns

Storage Layout

# Read private storage slot
cast storage <addr> <slot> --rpc-url <rpc>

Signature Replay

// Check nonce + chainId
bytes32 structHash = keccak256(abi.encode(nonce, to, amount));
bytes32 hash = keccak256(abi.encodePacked("\x19\x01", DOMAIN_SEPARATOR, structHash));

Frontrunning Simulation

// Mempool: see pending tx, front-run with higher gas
// Use Flashbots to hide tx

CTF References

• Ethernaut: OpenZeppelin's 30+ challenge set (standard reference)
• DeFi Security Summit 2024: Price oracle manipulation challenges
• Paradigm CTF 2024: Advanced flash loan + MEV challenges
• DownUnderCTF 2024: Solidity reentrancy with twist
• Blockchain CTF 2024: Cross-chain bridge analysis
• EclipseCTF 2025: SVM/EVM hybrid vulnerabilities
• corCTF 2025: L2 rollup state transition analysis
• HITCON CTF 2025: MEV bot analysis

Speed Metrics