CVE-2024-52304 is a vulnerability classified under CWE-444 (Inconsistent Interpretation of HTTP Requests), commonly known as HTTP request smuggling, affecting the aiohttp library, an asynchronous HTTP client/server framework for Python's asyncio. The root cause lies in the incorrect parsing of newlines within chunk extensions in HTTP requests by the pure Python parser used in aiohttp versions before 3.10.11. Specifically, when aiohttp is installed without its usual C extensions or when the environment variable AIOHTTP_NO_EXTENSIONS is set, the parser mishandles chunked transfer encoding, allowing attackers to craft specially formed HTTP requests that can be interpreted inconsistently by downstream servers, proxies, or firewalls. This inconsistency enables attackers to smuggle requests past security controls, potentially bypassing firewall rules or proxy protections. Exploitation does not require authentication or user interaction, and the attack vector is network-based. The CVSS 4.0 score of 6.3 reflects a medium severity, indicating moderate impact primarily on integrity and limited impact on confidentiality and availability. The vulnerability was publicly disclosed on November 18, 2024, and fixed in aiohttp version 3.10.11. No known exploits are reported in the wild as of now, but the presence of this vulnerability in widely used Python asynchronous web applications poses a tangible risk if left unpatched.

For European organizations, the vulnerability could allow attackers to bypass perimeter security controls such as firewalls and proxies that rely on consistent HTTP request parsing. This could lead to unauthorized access to internal services, manipulation of HTTP traffic, or injection of malicious requests, potentially compromising web applications or APIs built on aiohttp. The impact is particularly relevant for organizations deploying Python-based asynchronous web services, microservices, or API gateways using aiohttp without C extensions, which might be common in development or containerized environments. While the vulnerability does not directly lead to data leakage or denial of service, the ability to circumvent security controls can facilitate further attacks, including session hijacking or privilege escalation. Consequently, sectors with critical infrastructure, financial services, and cloud service providers in Europe could face increased risk if they do not promptly apply patches or mitigations.

European organizations should immediately upgrade aiohttp to version 3.10.11 or later to remediate this vulnerability. Where upgrading is not immediately feasible, disabling the use of the pure Python parser by ensuring C extensions are installed and enabled can reduce exposure. Review and audit configurations to avoid setting the environment variable AIOHTTP_NO_EXTENSIONS unless explicitly required. Network security teams should implement strict HTTP traffic inspection and validation at the perimeter, including anomaly detection for unusual chunked transfer encoding patterns. Application developers should conduct thorough testing of HTTP request handling, especially in asynchronous Python applications, to detect inconsistencies. Additionally, deploying Web Application Firewalls (WAFs) with updated signatures capable of detecting HTTP request smuggling attempts can provide an additional layer of defense. Monitoring logs for irregular HTTP request patterns and unusual proxy or firewall bypass attempts is also recommended.