Exploiting HTTP Request Smuggling

When to Use

During authorized penetration tests when the application sits behind a reverse proxy, load balancer, or CDN
When testing infrastructure with multiple HTTP processors in the request chain (nginx + Apache, HAProxy + Gunicorn)
For assessing applications for HTTP desynchronization vulnerabilities
When other attack vectors are limited and you need to bypass front-end security controls
During security assessments of multi-tier web architectures

Authorization: Written penetration testing agreement explicitly covering request smuggling (high-risk test)
Burp Suite Professional: With HTTP Request Smuggler extension (Turbo Intruder)
smuggler.py: Automated HTTP request smuggling detection tool
curl: Compiled with HTTP/1.1 support and manual chunked encoding
Target architecture knowledge: Understanding of proxy/server chain (front-end and back-end)
Caution: Request smuggling can affect other users' requests; test carefully