How to Detect VPNs with JavaScript

How to Detect VPNs with JavaScript

Detecting VPN usage has become increasingly important for websites and applications looking to prevent fraud, ensure compliance, or manage content access. While no method is foolproof, certain techniques can help identify VPN connections. In this article, we'll explore how to detect VPNs using JavaScript and provide some practical code snippets.

1. IP Address Checks

One of the primary methods to detect VPNs is by checking the user's IP address against known VPN servers. You can use an API service that maintains a list of VPN IP addresses.

Example Code:

async function isVPN(ipAddress) {
    const response = await fetch(`https://api.vpndetection.com/check?ip=${ipAddress}`);
    const data = await response.json();
    return data.isVPN; // Assuming the API returns an isVPN boolean
}

// Usage
const userIp = "192.0.2.1"; // Example IP
isVPN(userIp).then(isUsingVPN => {
    if (isUsingVPN) {
        console.log("User is connected via VPN.");
    } else {
        console.log("User is not using a VPN.");
    }
});

2. Geolocation Checks

Another way to detect VPN usage is by comparing the user’s geolocation with their reported IP address. If the geolocation does not match the IP address, it may indicate a VPN.

Example Code:

async function checkLocation(ipAddress) {
    const geoResponse = await fetch(`https://ipinfo.io/${ipAddress}/json`);
    const geoData = await geoResponse.json();
    return geoData;
}

// Usage
const userIp = "192.0.2.1"; // Example IP
checkLocation(userIp).then(geoData => {
    console.log("User Location:", geoData);
});

3. DNS Leak Tests

VPNs can sometimes leak DNS requests, which can expose a user’s actual location. You can perform a DNS leak test by checking the DNS servers being used.

Example Code:

function checkDNSLeak() {
    fetch('https://api.dnslookup.io/')
        .then(response => response.json())
        .then(data => {
            console.log("DNS Servers:", data.dns);
            // Check against known public DNS servers
            if (data.dns.includes("8.8.8.8") || data.dns.includes("1.1.1.1")) {
                console.log("Possible DNS leak detected.");
            } else {
                console.log("No DNS leak detected.");
            }
        })
        .catch(error => console.error("Error checking DNS:", error));
}

// Call the function
checkDNSLeak();

4. Behavioral Analysis

Users on a VPN may exhibit different browsing behaviors. For instance, rapid changes in geolocation or unusual access patterns could indicate VPN usage. While this method requires more complex analysis and tracking, it can provide additional insights.

Example Code (Pseudo Code):

let lastKnownLocation = null;

function analyzeBehavior(currentLocation) {
    if (lastKnownLocation && lastKnownLocation !== currentLocation) {
        console.log("Behavioral anomaly detected.");
    }
    lastKnownLocation = currentLocation;
}

// Call analyzeBehavior with the user's current location
analyzeBehavior("New York"); // Example

Conclusion

While detecting VPN usage with JavaScript can be challenging, combining various methods such as IP address checks, geolocation validation, DNS leak tests, and behavioral analysis can provide a more comprehensive approach. However, it's essential to remember that no method is infallible, and legitimate users might be affected by false positives.

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