
- by x32x01 ||
Understanding Web3 Vulnerabilities - A Deep Dive for Ethical Hackers
Web3 introduces a decentralized future, but with new power comes new attack surfaces. Let’s break down the most critical Web3 vulnerabilities, their real-world examples, and the tools used to detect/exploit them.
1. Re-Entrancy Attack
A classic vulnerability in Ethereum smart contracts.
The infamous DAO Hack (2016) resulted in the theft of ~3.6 million ETH.

PHP:
function withdraw(uint _amount) public {
if (balances[msg.sender] >= _amount) {
(bool success, ) = msg.sender.call{value: _amount}("");
require(success);
balances[msg.sender] -= _amount;
}
}


Mythril
Slither
Echidna (fuzzing)
2. Integer Overflow/Underflow
Before Solidity 0.8, arithmetic was unchecked.
Code:
uint8 x = 255;
x += 1; // x becomes 0 (overflow)


Slither
Manticore
3. Phishing via Web3 Wallets (Front-end Attacks)
Users tricked into signing malicious transactions via fake UI/popups.
Fake airdrop site asks user to “claim” tokens but actually steals all NFTs.

Browser dev tools
Metamask + testnet
4. Unprotected selfdestruct() Calls
Smart contracts can be killed if access control is misconfigured.
PHP:
function kill() public {
selfdestruct(payable(msg.sender));
}


Slither
Mythril
5. Oracle Manipulation Attacks
Manipulate price feeds to exploit DeFi protocols.
Flashloan used to temporarily inflate token price, borrow more than collateral worth.

Tenderly (debug transactions)
Foundry/Hardhat for simulations
Bonus: Common Testing Tools for Web3 Pentesters
Tool Use CaseSlither Static analysis of contracts
Mythril Vulnerability scanning
Echidna Fuzzing smart contracts
Tenderly Real-time monitoring/debugging
Foundry Contract development + testing
Remix IDE Manual testing/debugging

Web3 is powerful but not bulletproof. Every smart contract is a potential target. Always audit your contracts and test thoroughly before mainnet deployment.