# HTTP/1.1 Must Die: Conquering the 0.CL Challenge

DevFeed: [HTTP/1.1 Must Die: Conquering the 0.CL Challenge](<https://devfeed.tech/articles/http-1-1-must-die-conquering-the-0-cl-challenge-7725.md>)

Original publisher: [Read original article](<https://portswigger.net/blog/http-1-1-must-die-conquering-the-0-cl-challenge>)

Author: Fran Hutchings

Published: 2026-03-13T09:21:19Z

Content type: article

Language: en

Sources: [PortSwigger Blog](<https://devfeed.tech/sources/portswigger-blog.md>)

Topics: [Security](<https://devfeed.tech/topics/security.md>), [Parser](<https://devfeed.tech/topics/parser.md>), [payload](<https://devfeed.tech/topics/payload.md>), [Extension](<https://devfeed.tech/topics/extension.md>), [Script](<https://devfeed.tech/topics/script.md>)

Tags: [article](<https://devfeed.tech/tags/article.md>), [extension](<https://devfeed.tech/tags/extension.md>), [http](<https://devfeed.tech/tags/http.md>), [payload](<https://devfeed.tech/tags/payload.md>), [security](<https://devfeed.tech/tags/security.md>), [techniques](<https://devfeed.tech/tags/techniques.md>), [tools](<https://devfeed.tech/tags/tools.md>)

## AI overview

A technical guide to the 0.CL variant of HTTP request smuggling, explaining the front-end/back-end parsing discrepancy, four proof-of-concept approaches, and detection with PortSwigger's HTTP Request Smuggler extension in a controlled lab.

## Source excerpt

Note: This is a guest post by pentester Julen Garrido Estévez (@b3xal). 1. Acknowledgements 2. Intro 3. Required tools 4. Strategy to solve/exploit the lab 5. Detecting 0.CL 5.1. Practical confirmatio