HTTP Connection Request Smuggling

👉 Overview

👀 What ?

HTTP Connection Request Smuggling (CRS) is a high-level, complex web security vulnerability that can exploit discrepancies in the handling of HTTP requests between web servers and proxy servers. This vulnerability enables an attacker to smuggle a malformed HTTP request through a proxy server to another backend server, bypassing security controls and potentially gaining unauthorized access to sensitive data.

🧐 Why ?

CRS is a significant security issue because it can bypass many standard security measures, such as firewalls and intrusion detection systems, and it can be used to carry out a variety of malicious activities, including data theft, session hijacking, or even remote code execution. Furthermore, CRS attacks can be difficult to detect and mitigate due to their complex nature and the fact they exploit a fundamental aspect of web architecture.

⛏️ How ?

To exploit CRS, an attacker sends a series of specially crafted HTTP requests to a vulnerable server. The first request appears to be legitimate and is passed by the proxy server, but it contains a hidden, second request, which is smuggled through to the backend server. The backend server then interprets this second request as a separate, legitimate request, potentially leading to unauthorized actions. To defend against CRS, organizations should ensure their servers are correctly configured to handle HTTP requests and should regularly update and patch their systems to protect against known vulnerabilities.

⏳ When ?

CRS attacks have been known to the cybersecurity community since the early 2000s, but they have gained more attention in recent years due to the increasing reliance on web-based services and the proliferation of sophisticated attack tools.

⚙️ Technical Explanations

In a CRS attack, the attacker manipulates the HTTP 'Content-Length' and 'Transfer-Encoding' headers in a way that causes a discrepancy in the interpretation of HTTP requests between the proxy and the backend server. This discrepancy allows the attacker to prepend or append malicious content to legitimate HTTP requests, which can then be executed on the backend server. The complex nature of these attacks, combined with the fundamental role of HTTP in web architecture, makes CRS a challenging issue to address. Mitigation strategies typically involve ensuring strict adherence to HTTP specifications and implementing robust error handling and anomaly detection mechanisms.