Critical HTTP Request Smuggling Vulnerability in Kestrel (CVE-2025-55315) Exposes ASP.NET Applications

A critical vulnerability, CVE-2025-55315, has been identified in ASP.NET's Kestrel web server, enabling HTTP Request Smuggling through chunk extensions. This vulnerability, discovered by a security researcher and rewarded with a $10,000 bounty, poses significant risks to ASP.NET applications. HTTP Request Smuggling allows attackers to manipulate HTTP requests, potentially leading to session hijacking, cache poisoning, and unauthorized data access. The vulnerability stems from improper handling of chunk extensions in Kestrel, a cross-platform web server for ASP.NET Core. Chunk extensions, part of the HTTP/1.1 protocol, can be exploited to craft malicious requests. Organizations using Kestrel should immediately update their systems to the latest version to mitigate this risk. Additionally, monitoring for unusual HTTP traffic patterns can help detect and prevent exploitation attempts. This discovery underscores the importance of securing HTTP protocols and the value of bug bounty programs in enhancing software security. The impact on the cybersecurity landscape is substantial, as Kestrel is widely used in ASP.NET Core applications. Cybersecurity professionals should prioritize patching and monitoring to protect against potential attacks exploiting this vulnerability.