⚠️ Note This content is meant purely for learning and research purposes. Avoid testing vulnerabilities on public blockchains. Always follow responsible disclosure practices when identifying bugs in smart contracts. 👋 Hello everyone, I’m Vinay Sati — a Bug Bounty Hunter, Forensic Investigator, and Web3 Security Tester. I consider myself a versatile cybersecurity professional, passionate about finding vulnerabilities, securing smart contracts, and investigating digital threats. In this article, I’ll share a real example of a Web3 exploit and show you how to identify and prevent such risks. Introduction In blockchain development, smart contracts may encounter serious vulnerabilities, especially when: There’s a loop that iterates over data provided by users
The array input length is not limited
Proper permissions or access control are missing There’s a loop that iterates over data provided by users The array input length is not limited Proper permissions or access control are missing These issues can result in the contract becoming unusable, gas being wasted, or potential abuse by malicious actors. Let's look at a clear example of this kind of vulnerability, along with a simplified code sample. Vulnerable Smart Contract Example Below is a contract that simulates a basic batch airdrop. However, it contains a key flaw: 💀 What Could Go Wrong? No restriction on who can call the airdrop() function. No limit on the number of addresses passed into the function. Someone could pass in thousands of addresses, causing the loop to consume all available gas. This can disable the contract's functionality or cause ETH to be locked due to failed execution. 🧪 Simulating the Exploit (In a Test Environment) Here’s an example using a development framework that demonstrates how this kind of exploit might occur: 🛡️ How Can This Be Fixed? ✅ Add Access Restrictions Update the vulnerable function like this: 🧯 Summary of Fixes Fix

Purpose



Add onlyOwner modifier

Prevent unauthorized access to core logic



Add input length check

Avoid gas exhaustion through oversized loops



Consider off-chain batching

Handle large distributions more safely Fix

Purpose



Add onlyOwner modifier

Prevent unauthorized access to core logic



Add input length check

Avoid gas exhaustion through oversized loops



Consider off-chain batching

Handle large distributions more safely Fix

Purpose Fix Fix Purpose Purpose Add onlyOwner modifier

Prevent unauthorized access to core logic Add onlyOwner modifier Add onlyOwner modifier onlyOwner Prevent unauthorized access to core logic Prevent unauthorized access to core logic Add input length check

Avoid gas exhaustion through oversized loops Add input length check Add input length check Avoid gas exhaustion through oversized loops Avoid gas exhaustion through oversized loops Consider off-chain batching

Handle large distributions more safely Consider off-chain batching Consider off-chain batching Handle large distributions more safely Handle large distributions more safely 📸 Visual Aids (Optional for Reports) Attack Flow Diagram: User ➜ Calls vulnerable function ➜ Contract loops ➜ Exceeds gas ➜ Fails


Before vs. After code comparison (highlighting secure access control) Attack Flow Diagram: User ➜ Calls vulnerable function ➜ Contract loops ➜ Exceeds gas ➜ Fails Attack Flow Diagram: User ➜ Calls vulnerable function ➜ Contract loops ➜ Exceeds gas ➜ Fails Attack Flow Diagram Before vs. After code comparison (highlighting secure access control) Before vs. After code comparison (highlighting secure access control) Before vs. After 🚀 Real Examples Project

Vulnerability

Outcome



Akropolis

Reentrancy + logic flaw

~$2M lost



Bancor

Infinite loop DoS

250 ETH bounty awarded



DYDX

Gas griefing + front-running

Resolved via bug report Project

Vulnerability

Outcome



Akropolis

Reentrancy + logic flaw

~$2M lost



Bancor

Infinite loop DoS

250 ETH bounty awarded



DYDX

Gas griefing + front-running

Resolved via bug report Project

Vulnerability

Outcome Project Project Vulnerability Vulnerability Outcome Outcome Akropolis

Reentrancy + logic flaw

~$2M lost Akropolis Akropolis Reentrancy + logic flaw Reentrancy + logic flaw ~$2M lost ~$2M lost Bancor

Infinite loop DoS

250 ETH bounty awarded Bancor Bancor Infinite loop DoS Infinite loop DoS 250 ETH bounty awarded 250 ETH bounty awarded DYDX

Gas griefing + front-running

Resolved via bug report DYDX DYDX Gas griefing + front-running Gas griefing + front-running Resolved via bug report Resolved via bug report 🙌 Final Thoughts Even basic oversights like failing to limit array sizes or restricting function access can result in major vulnerabilities. Taking the time to audit code, simulate edge cases, and follow best practices helps protect users and build trust in decentralized systems.

Exploring a Web3 Smart Contract Issue: Gas Exploitation via Unchecked Loops

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