HTTP request smuggling is a vulnerability type that allows an attacker to bypass security protections, conduct phishing attacks, and obtain sensitive information from requests other than their own. It exploits deviations from the HTTP/1.1 protocol specifications, particularly in how keep-alive, pipelining, content length, and transfer encoding are handled by frontend and backend libraries. The vulnerability can be exploited through two common techniques: CL:CL (Double Content-Length) attack technique and CL:TE (Content-Length Transfer-Encoding) attack technique. Remediation involves prioritizing the transfer-encoding header over content-length, disallowing requests with both headers, and ensuring proper processing of multiple transfer encoding values. The vulnerability affects both frontend and backend projects, requiring a defense-in-depth approach to patch against it.