Imagine hitting a website with a sneaky request that slips past its defenses, letting you bypass authentication or poison its cache. That’s HTTP request smuggling — a powerful, under-discussed vulnerability that’s earning bug hunters $5,000+ bounties in 2025. As modern web apps rely on proxies and load balancers, desyncs between HTTP/1.1 and HTTP/2 create gaps attackers can exploit. This beginner-friendly guide, inspired by NahamSec and James Kettle’s research, shows you how to find and exploit HTTP request smuggling using Burp Suite. We’ll walk through spotting vulnerable setups, crafting malicious requests, and reporting bugs for big rewards. Whether you’re new or a pro, let’s smuggle your way to bug bounty success!

Why HTTP Request Smuggling Matters

HTTP request smuggling exploits mismatches in how frontend (e.g., Cloudflare) and backend servers parse HTTP requests, often due to ambiguous headers like Content-Length or Transfer-Encoding. Common types (CL.TE, TE.CL) can lead to:

• Authentication Bypasses: Access restricted endpoints.
• Cache Poisoning: Serve malicious…