- by x32x01 ||
Web3 is shaping a decentralized future, but with innovation comes new security risks ⚠️. Smart contracts are immutable, public, and often handle millions of dollars - which makes them a prime target for attackers.
In this guide, we’ll break down the most common Web3 vulnerabilities, real-world examples, and the tools ethical hackers use to find and test them 🧠💻.
A re-entrancy attack happens when a contract sends funds before updating its internal state, allowing attackers to repeatedly drain funds.
🧪 Real-world example:
The DAO Hack (2016), where attackers stole around 3.6 million ETH 😱.
🛠️ Vulnerable code example:
👨💻 An attacker creates a fallback function that keeps calling withdraw() before the balance updates.
🧰 Testing tools:
🧪 Example:
This can break logic and allow attackers to bypass limits or drain funds.
✅ New Solidity versions fix this automatically, but legacy contracts are still risky.
🧰 Tools to detect it:
Attackers trick users into signing malicious transactions through fake websites or popups.
🧪 Example:
A fake airdrop page asks users to “claim tokens” - but actually drains their wallet or NFTs 💸.
🔧 Analysis tools:
🧪 Bad example:
👨💻 Without an onlyOwner modifier, attackers can permanently kill the contract.
🧰 Detection tools:
🧪 Example:
Using flash loans to temporarily manipulate token prices, then borrowing more than the collateral is worth.
🧰 Testing & simulation tools:
If you’re building or auditing Web3 apps:
In this guide, we’ll break down the most common Web3 vulnerabilities, real-world examples, and the tools ethical hackers use to find and test them 🧠💻.
Re-Entrancy Attacks 🧨
One of the most famous smart contract vulnerabilities, especially on Ethereum.A re-entrancy attack happens when a contract sends funds before updating its internal state, allowing attackers to repeatedly drain funds.
🧪 Real-world example:
The DAO Hack (2016), where attackers stole around 3.6 million ETH 😱.
🛠️ Vulnerable code example:
C:
function withdraw(uint _amount) public {
if (balances[msg.sender] >= _amount) {
(bool success, ) = msg.sender.call{value: _amount}("");
require(success);
balances[msg.sender] -= _amount;
}
}🧰 Testing tools:
- Slither
- Mythril
- Echidna (fuzz testing)
Integer Overflow & Underflow 🔐
Older Solidity versions (before 0.8) didn’t check arithmetic limits.🧪 Example:
C:
uint8 x = 255;
x += 1; // overflow → x becomes 0✅ New Solidity versions fix this automatically, but legacy contracts are still risky.
🧰 Tools to detect it:
- Slither
- Manticore
Web3 Phishing & Wallet Attacks 🪤
Not all attacks are on-chain - many target the frontend 😬.Attackers trick users into signing malicious transactions through fake websites or popups.
🧪 Example:
A fake airdrop page asks users to “claim tokens” - but actually drains their wallet or NFTs 💸.
🔧 Analysis tools:
- Browser DevTools
- MetaMask (with testnets)
Unprotected selfdestruct() Calls 📬
If access control is missing, anyone can destroy a contract.🧪 Bad example:
Code:
function kill() public {
selfdestruct(payable(msg.sender));
}👨💻 Without an onlyOwner modifier, attackers can permanently kill the contract.
🧰 Detection tools:
- Slither
- Mythril
Oracle Manipulation Attacks 🕳️
DeFi apps rely on price oracles - and attackers love that 😈.🧪 Example:
Using flash loans to temporarily manipulate token prices, then borrowing more than the collateral is worth.
🧰 Testing & simulation tools:
- Tenderly (transaction debugging)
- Foundry / Hardhat
Essential Web3 Testing Tools 🧪🧰
| Tool | Use Case |
|---|---|
| Slither | Static smart contract analysis |
| Mythril | Automated vulnerability scanning |
| Echidna | Smart contract fuzzing |
| Tenderly | Real-time debugging & monitoring |
| Foundry | Testing & development framework |
| Remix IDE | Manual testing & debugging |
Final Thoughts 🚨
Web3 is powerful - but not bulletproof. Every smart contract is a potential attack surface.If you’re building or auditing Web3 apps:
- Test early 🧪
- Audit thoroughly 🔍
- Never deploy to mainnet without confidence 🚀
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