HTTP Response Smuggling / Desync

👉 Overview

👀 What ?

HTTP Response Smuggling, also known as Desync, is a type of web application vulnerability that allows an attacker to inject malicious content into HTTP responses received by other users. This is achieved by manipulating the way web servers process HTTP requests, causing them to 'desync' from the correct state and interpret requests incorrectly.

🧐 Why ?

Understanding HTTP Response Smuggling is vital as it presents a significant security risk. Attackers exploiting this vulnerability can bypass security controls, compromise user data, and potentially gain unauthorized access to systems. As HTTP is the foundation of data communication on the World Wide Web, any vulnerability in its implementation can have wide-reaching implications.

⛏️ How ?

To prevent HTTP Response Smuggling, developers and system administrators should ensure that all HTTP headers are correctly validated and sanitized before being processed. Additionally, implementing a web application firewall (WAF) can help to detect and block attempts to exploit this vulnerability. Regularly updating and patching software can also mitigate the risk.

⏳ When ?

HTTP Response Smuggling was first identified and named as a distinct vulnerability class in the early 2000s. Despite the widespread awareness and available mitigation techniques, it remains a commonly encountered vulnerability in modern web applications due to the complexity of HTTP and the multitude of systems involved in processing HTTP requests.

⚙️ Technical Explanations

HTTP Response Smuggling exploits discrepancies in how different systems process HTTP headers. For instance, if a server uses the 'Content-Length' header to determine the end of a response, but a proxy uses the 'Transfer-Encoding: chunked' header, an attacker could manipulate these headers to cause the server and the proxy to disagree on where one response ends and another begins. This disagreement, or 'desync', allows the attacker to prepend malicious content to the responses of other users.