CVE-2022-24801 is a vulnerability in the Twisted Web HTTP 1.1 server, part of the Twisted event-driven networking engine for Python (versions up to 22.2.0). The flaw arises from the server's lenient and non-RFC 7230-compliant parsing of certain HTTP request constructs. Specifically, the twisted.web.http module does not strictly enforce the HTTP/1.1 protocol parsing rules, which can cause inconsistent interpretation of HTTP requests when these requests traverse multiple HTTP parsers or proxies. This inconsistency can lead to HTTP request smuggling attacks, where an attacker crafts specially malformed HTTP requests that are interpreted differently by front-end and back-end servers or proxies. Such desynchronization allows attackers to bypass security controls, poison web caches, hijack user sessions, or perform cross-site scripting and web cache poisoning. The vulnerability affects only the HTTP 1.1 server and proxy components of Twisted; the HTTP 2.0 server and the Twisted Web client are not impacted. Exploitation requires that the vulnerable Twisted HTTP server be used in conjunction with other HTTP servers or proxies that parse requests differently, creating the conditions for request smuggling. The issue was fixed in Twisted version 22.4.0rc1. Mitigation options include upgrading Twisted to this or a later version, ensuring upstream proxies are patched against similar vulnerabilities, or filtering malformed requests at the proxy or firewall level. There are no known exploits in the wild as of the publication date, but the nature of HTTP request smuggling vulnerabilities makes them a significant risk in complex web infrastructure environments where multiple HTTP parsers coexist.

For European organizations, the impact of this vulnerability can be significant, especially for those relying on Twisted Web HTTP 1.1 servers in multi-proxy or multi-server environments. HTTP request smuggling can lead to unauthorized access, session hijacking, web cache poisoning, and bypass of security controls such as WAFs or authentication mechanisms. This can compromise the confidentiality and integrity of sensitive data, disrupt service availability, and facilitate further attacks such as cross-site scripting or injection attacks. Organizations in sectors with high reliance on web applications and APIs—such as finance, healthcare, telecommunications, and government—are particularly at risk. The complexity of European IT infrastructures, often involving layered proxies and load balancers, increases the likelihood of exploitable desynchronization. Additionally, compliance with GDPR and other data protection regulations means that exploitation leading to data breaches could result in severe legal and financial penalties. Although no active exploitation is currently reported, the medium severity rating and the potential for stealthy attacks warrant proactive remediation.

Upgrade all Twisted Web HTTP 1.1 server instances to version 22.4.0rc1 or later to apply the official patch addressing the parsing inconsistency. Audit and upgrade upstream HTTP proxies and servers to versions that are not vulnerable to HTTP request smuggling, ensuring consistent and RFC-compliant HTTP parsing across the request chain. Implement strict input validation and filtering at the network edge (e.g., web application firewalls or reverse proxies) to detect and block malformed or suspicious HTTP requests that could trigger desynchronization. Conduct thorough testing of multi-proxy and multi-server HTTP request handling to identify and remediate any inconsistencies in request parsing behavior. Monitor HTTP traffic logs for anomalies indicative of request smuggling attempts, such as unexpected request lengths, duplicated headers, or unusual request sequences. Educate development and operations teams about the risks of HTTP request smuggling and the importance of consistent HTTP parsing in complex web architectures. Where feasible, consider migrating critical services to HTTP/2 or later protocols, which use different parsing mechanisms not affected by this vulnerability.