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Xavier Fok
Xavier Fok

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DNS and WebRTC Leaks: The Hidden Proxy Killers

#proxy #security #webdev #networking

You have set up your proxy perfectly. Your IP shows the right location. But your real identity is leaking through DNS queries and WebRTC connections. These invisible leaks are responsible for more account bans than most operators realize.

What Are DNS Leaks?

How DNS Works

When you visit a website, your browser first asks a DNS server to translate the domain name into an IP address. This DNS query happens before the actual web request.

The Leak

Many proxy configurations only route web traffic through the proxy. DNS queries bypass the proxy and go directly to your ISP DNS server, revealing:

  • Your real ISP — Identifies your actual internet provider
  • Your real location — ISP DNS servers are geographically located near you
  • Your browsing history — Every domain you visit is logged by the DNS server 
Without DNS leak:
Browser → Proxy → DNS Server → Website
(Everything goes through proxy)

With DNS leak:
Browser → ISP DNS Server (LEAK!)
Browser → Proxy → Website
(DNS bypasses proxy)
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How to Detect DNS Leaks

Visit a DNS leak test site through your proxy. If the results show your real ISP or location instead of the proxy location, you have a DNS leak.

How to Fix DNS Leaks

1. Use proxy-level DNS resolution:

Configure your proxy to handle DNS queries:

import requests

# SOCKS5 proxy with remote DNS resolution
proxy = {
    "http": "socks5h://user:pass@proxy:1080",  # Note the h for DNS through proxy
    "https": "socks5h://user:pass@proxy:1080"
}
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The socks5h:// protocol (note the h) tells the client to send DNS queries through the SOCKS5 proxy instead of resolving locally.

2. Configure system DNS:

Point your system DNS to the proxy location:

# Use DNS servers matching your proxy location
# For US proxies:
nameserver 8.8.8.8
nameserver 1.1.1.1
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3. Use anti-detect browser DNS settings:

Most anti-detect browsers have built-in DNS leak protection. Enable it in profile settings.

What Are WebRTC Leaks?

How WebRTC Works

WebRTC (Web Real-Time Communication) enables peer-to-peer connections for video calls, voice chat, and file sharing in browsers. To establish these connections, it uses STUN and TURN servers.

The Leak

WebRTC can discover your real IP address — even behind a proxy — by querying STUN servers:

// This runs silently in the browser
const pc = new RTCPeerConnection({
    iceServers: [{urls: "stun:stun.l.google.com:19302"}]
});

pc.createDataChannel("");
pc.createOffer().then(offer => pc.setLocalDescription(offer));

pc.onicecandidate = (event) => {
    if (event.candidate) {
        // This candidate string contains your REAL IP
        const ip = event.candidate.candidate
            .split(" ")[4];
        console.log("Real IP exposed:", ip);
    }
};
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Platforms can run this code without your knowledge and compare the WebRTC IP to your proxy IP. If they differ, you are flagged.

Types of WebRTC Leaks

  1. Public IP leak — Your real public IP is exposed
  2. Local IP leak — Your local network IP (192.168.x.x) is exposed, which can be used for fingerprinting
  3. mDNS leak — Some browsers use mDNS to mask local IPs, but implementation varies

How to Fix WebRTC Leaks

Option 1: Disable WebRTC entirely

In Firefox:

about:config → media.peerconnection.enabled → false
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Option 2: Use anti-detect browsers

Anti-detect browsers offer WebRTC handling options:

  • Disabled — No WebRTC functionality
  • Altered — WebRTC shows the proxy IP instead of real IP
  • Real — Uses actual WebRTC (only for profiles that need video calls)

Option 3: Browser extensions

Extensions like WebRTC Leak Shield can block WebRTC IP exposure in regular browsers.

Other Hidden Leaks

IPv6 Leaks

Your proxy handles IPv4 traffic, but IPv6 requests bypass it:

# Disable IPv6 on Linux
sudo sysctl -w net.ipv6.conf.all.disable_ipv6=1
sudo sysctl -w net.ipv6.conf.default.disable_ipv6=1
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HTTP Header Leaks

Some proxies add headers that reveal proxy usage:

  • X-Forwarded-For — Contains your real IP
  • Via — Indicates proxy usage
  • X-Real-IP — Your actual IP

Use elite/anonymous proxies that strip these headers.

Timezone Leaks

JavaScript can read your system timezone:

Intl.DateTimeFormat().resolvedOptions().timeZone
// Returns: "America/New_York" even if proxy is in London
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Always match your system timezone to your proxy location.

Complete Leak Prevention Checklist

  • [ ] DNS queries route through proxy (use socks5h://)
  • [ ] WebRTC disabled or showing proxy IP
  • [ ] IPv6 disabled or routed through proxy
  • [ ] No X-Forwarded-For or Via headers
  • [ ] Timezone matches proxy location
  • [ ] Language settings match proxy location
  • [ ] GPS coordinates disabled or spoofed (mobile)

For comprehensive proxy leak prevention guides, visit DataResearchTools.

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