CVE-2022-24761 is a vulnerability classified under CWE-444, involving inconsistent interpretation of HTTP requests, commonly known as HTTP Request Smuggling, affecting the Waitress web server. Waitress is a Python-based Web Server Gateway Interface (WSGI) server widely used to serve Python web applications. The vulnerability exists in Waitress versions prior to 2.1.1 and arises when Waitress is deployed behind a front-end proxy that does not strictly validate HTTP requests according to the RFC7230 standard. The core issue is that Waitress and the proxy may interpret the boundaries of HTTP requests differently, allowing an attacker to smuggle malicious requests through the proxy to the backend server. Two main technical flaws contribute to this: first, Waitress uses Python's int() function to parse Content-Length headers, which incorrectly accepts strings like '+10' or '0x01' as valid integers (parsing them as 10 and 1 respectively), whereas RFC7230 requires the Content-Length to be strictly digits only. Second, Waitress does not support chunked transfer encoding extensions but discards them without validating their content, potentially allowing illegal characters to pass unchecked. This discrepancy can be exploited to craft specially formed HTTP requests that confuse the proxy and Waitress about request boundaries, enabling attackers to bypass security controls, poison caches, or perform cross-user attacks. Although no known exploits are reported in the wild, the vulnerability has been patched in Waitress version 2.1.1. As a workaround, users are advised to configure front-end proxies to strictly enforce RFC7230 compliance on incoming requests, though not all proxies support this feature. Upgrading Waitress to the fixed version is the recommended remediation.

For European organizations, this vulnerability poses a moderate risk primarily to web applications and services that use Waitress behind proxies that do not enforce strict HTTP request validation. Successful exploitation could allow attackers to smuggle malicious requests, potentially leading to unauthorized actions such as session hijacking, cache poisoning, request forgery, or bypassing security controls. This could compromise confidentiality by leaking sensitive data, integrity by manipulating requests or responses, and availability if the attack disrupts normal service operation. Organizations in sectors with high reliance on Python-based web infrastructure—such as technology firms, financial services, healthcare, and public administration—may face increased risk. The impact is heightened in environments where proxies are misconfigured or lack strict RFC7230 enforcement. Although no active exploitation is currently known, the subtlety of HTTP request smuggling attacks means detection can be difficult, increasing the risk of undetected compromise. Given the widespread use of proxies and Python web servers in Europe, the vulnerability could affect a broad range of services if not mitigated.

To mitigate this vulnerability, European organizations should: 1) Immediately upgrade Waitress to version 2.1.1 or later, which contains the patch addressing the parsing and chunk extension validation issues. 2) Audit and configure all front-end proxies (e.g., Nginx, HAProxy, Apache HTTP Server) to enforce strict compliance with RFC7230, particularly validating Content-Length headers and rejecting malformed or ambiguous HTTP requests. 3) Where proxies lack built-in strict validation, consider deploying additional HTTP request validation tools or web application firewalls (WAFs) capable of detecting and blocking request smuggling attempts. 4) Conduct thorough testing of proxy and backend server interactions to identify any discrepancies in request parsing behavior. 5) Monitor logs for anomalies indicative of request smuggling, such as unexpected request boundaries or unusual header formats. 6) Educate development and operations teams about HTTP request smuggling risks and ensure secure coding and deployment practices. 7) Implement defense-in-depth by combining proxy validation, patched backend servers, and runtime detection mechanisms to reduce attack surface. These steps go beyond generic advice by focusing on proxy configuration specifics and operational monitoring tailored to this vulnerability.