If you run any kind of public API, SaaS, or forum, you already know the pain: Bot traffic.
You ban a user for spamming, and 5 seconds later they are back with a new account because they toggled their VPN. You block an IP, and they switch to a Tor exit node.
In this tutorial, I'm going to show you how to detect Non-Residential IPs (VPNs, Proxies, and Hosting Centers) in your Node.js application so you can block them—or at least challenge them with a CAPTCHA—before they touch your database.
The Goal
We want a middleware function in Express that looks like this:
javascript
app.use((req, res, next) => {
if (isHighRisk(req.ip)) {
return res.status(403).send("VPNs are not allowed.");
}
next();
});
Here is how to build it.
Method 1: The "Hard" Way (Self-Hosted Lists)
If you want to do this entirely for free and offline, you need to download and maintain lists of known "Bad IPs."
Step 1: Get the Data
You will need to find a text file of Tor Exit nodes and IP ranges for major cloud providers (AWS, DigitalOcean, Linode).
Tor Exit Nodes: The Tor project publishes a list of exit addresses.
Cloud Ranges: AWS and Google publish their IP ranges in massive JSON files.
Step 2: The Code
You'll need to parse these lists into memory and check every incoming request.
JavaScript
const fs = require('fs');
const ipRangeCheck = require('ip-range-check'); // You'll need this npm package
// 1. Load the massive lists into memory (Careful with RAM!)
const torNodes = fs.readFileSync('tor-exit-nodes.txt', 'utf8').split('\n');
const awsRanges = JSON.parse(fs.readFileSync('aws-ip-ranges.json', 'utf8')).prefixes.map(p => p.ip_prefix);
function isHighRisk(userIp) {
// Check if IP is in the Tor list
if (torNodes.includes(userIp)) return true;
// Check if IP is in a Cloud Range (CPU intensive)
if (ipRangeCheck(userIp, awsRanges)) return true;
return false;
}
The Problem with Method 1
Stale Data: VPN providers rotate IPs daily. If you don't update your lists every hour, you will miss attacks.
Memory Hog: Loading millions of IPs into Node.js memory can crash your server (I learned this the hard way and OOM-killed my $5 droplet).
False Positives: It's hard to distinguish between a "Good" data center IP and a "Bad" VPN.
Method 2: The "Easy" Way (Live API Lookup)
After struggling with maintaining my own lists, I built a dedicated API called CandyCornDB to handle the heavy lifting. It specifically targets Infrastructure (ASN/ISP data) rather than just "bad behavior," so it catches fresh VPNs instantly.
Here is how to implement it in 3 lines of code.
Step 1: Get a Free API Key
You can grab a free key here (no credit card required).
Step 2: The Middleware
We will query the API, which returns a trustScore (0-100).
0-50: Residential / Safe
75+: High Risk (VPN / Tor / Hosting)
JavaScript
const axios = require('axios');
async function checkRiskScore(req, res, next) {
const userIp = req.ip;
try {
const response = await axios.get('[https://candycorndb.com/api/public/ip-score](https://candycorndb.com/api/public/ip-score)', {
params: { ip: userIp }
});
const { score, isTor, isVPN } = response.data;
// BLOCK if it's a confirmed Tor node or very high risk
if (isTor || score > 85) {
return res.status(403).json({ error: 'Anonymizers not allowed.' });
}
// CHALLENGE if it's suspicious (e.g., DigitalOcean droplet)
if (score >= 50) {
// Logic to show a CAPTCHA goes here...
console.log(`Suspicious traffic from ${userIp}`);
}
next();
} catch (err) {
// Fail open: If API is down, let the user in so you don't block real people
next();
}
}
// Apply to your sensitive routes
app.post('/api/signup', checkRiskScore, (req, res) => {
res.send("Account created!");
});
Why this is better
Just-in-Time Scanning: If the API hasn't seen the IP before, it scans open ports and ISP data in <500ms. You never get "Unknown."
No Maintenance: You don't need to download daily CSV dumps.
Saves RAM: Your Node server handles the logic, not the database storage.
Summary
Blocking bad IPs is an arms race. If you are building a small hobby project, Method 1 is a fun learning exercise. But if you are protecting a production app, offloading the risk detection to a dedicated API (Method 2) is usually cheaper than the time you'll spend unbanning spam accounts.
Let me know if you have questions about IP filtering logic! I've spent way too much time staring at ASN lists lately. 😅
SOCIAL SHARE CARD GENERATOR