CVE-2024-23829 is a vulnerability classified under CWE-444 (Inconsistent Interpretation of HTTP Requests), commonly known as HTTP Request/Response Smuggling, found in the aiohttp framework versions before 3.9.2. aiohttp is widely used for asynchronous HTTP client and server implementations in Python, leveraging asyncio. The vulnerability stems from minor discrepancies in the HTTP parser's handling of allowable character sets and error handling mechanisms. Specifically, the parser's leniency in accepting characters that should trigger error handling can cause inconsistent frame boundary detection in HTTP proxies, allowing attackers to smuggle additional HTTP requests into the communication stream. Furthermore, certain malformed inputs trigger exceptions that are not uniformly handled, potentially leading to excessive resource consumption on the application server or its logging systems, which could degrade availability. This issue is a regression or incomplete fix of CVE-2023-47627, indicating that prior remediation efforts did not fully address the underlying parsing inconsistencies. The vulnerability can be exploited remotely without authentication or user interaction, making it accessible to unauthenticated attackers. The CVSS v3.1 score of 6.5 reflects a medium severity, with network attack vector, low attack complexity, no privileges required, and no user interaction needed. The impact primarily affects the integrity of HTTP communications and availability of services due to resource exhaustion. The fix is included in aiohttp version 3.9.2, which corrects the parsing logic and exception handling to align with internet standards and robustly enforce frame boundaries.

For European organizations, the vulnerability poses a risk to web applications and services built on aiohttp versions prior to 3.9.2. HTTP request smuggling can allow attackers to bypass security controls, poison web caches, hijack user sessions, or conduct web cache deception attacks, undermining data integrity and confidentiality indirectly. Additionally, the unhandled exceptions causing resource exhaustion could lead to denial of service conditions, impacting service availability. Organizations in sectors such as finance, healthcare, government, and critical infrastructure that rely on Python-based asynchronous web frameworks are particularly vulnerable. The attack can be launched remotely without authentication, increasing the threat surface. Given the widespread use of Python and aiohttp in modern web services, the vulnerability could affect cloud services, APIs, and proxy servers deployed across Europe. The impact is heightened in environments where aiohttp is used as a reverse proxy or gateway, as request smuggling can manipulate downstream server behavior. Failure to patch could lead to exploitation attempts that disrupt business operations, degrade user trust, and potentially expose sensitive data through indirect attack vectors.

The primary mitigation is to upgrade all aiohttp deployments to version 3.9.2 or later, where the vulnerability has been fixed. Organizations should audit their software inventories to identify affected versions and prioritize patching in production and development environments. Beyond patching, implement strict HTTP request validation at the application and proxy layers to detect and block malformed or suspicious requests that could be used for request smuggling. Deploy Web Application Firewalls (WAFs) with updated signatures capable of detecting HTTP request smuggling patterns. Monitor server and application logs for anomalies such as unexpected exceptions or resource usage spikes indicative of exploitation attempts. Conduct penetration testing focused on HTTP request smuggling to validate defenses. For proxy and gateway configurations, ensure consistent parsing and error handling policies to prevent discrepancies that facilitate smuggling. Educate development and operations teams about the risks of inconsistent HTTP parsing and the importance of adhering to internet standards. Finally, maintain an incident response plan that includes detection and mitigation of HTTP request smuggling attacks.