CVE-2024-52304 in aiohttp
Summary
by MITRE • 11/18/2024
aiohttp is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.10.11, the Python parser parses newlines in chunk extensions incorrectly which can lead to request smuggling vulnerabilities under certain conditions. If a pure Python version of aiohttp is installed (i.e. without the usual C extensions) or `AIOHTTP_NO_EXTENSIONS` is enabled, then an attacker may be able to execute a request smuggling attack to bypass certain firewalls or proxy protections. Version 3.10.11 fixes the issue.
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Analysis
by VulDB Data Team • 08/15/2025
The vulnerability identified as CVE-2024-52304 affects the aiohttp asynchronous HTTP client/server framework for Python, specifically targeting the parsing behavior of chunk extensions in HTTP requests. This issue manifests in versions prior to 3.10.11 where the Python parser incorrectly handles newline characters within chunk extensions, creating a potential avenue for request smuggling attacks. The vulnerability is particularly significant because it exploits a fundamental parsing mechanism that governs how HTTP chunked transfer encoding is processed, which is a core component of the HTTP protocol implementation.
The technical flaw resides in the improper parsing of chunk extensions that occur after the chunk size in HTTP transfer encoding. When the pure Python implementation of aiohttp is used or when the AIOHTTP_NO_EXTENSIONS environment variable is set, the framework falls back to a Python-only parser that does not correctly interpret newline characters within chunk extensions. This parsing error creates ambiguity in how the HTTP parser interprets the boundaries between chunks, potentially allowing an attacker to manipulate the request structure. According to CWE-129, this vulnerability relates to improper handling of input boundaries, specifically within the context of HTTP protocol parsing where incorrect boundary detection can lead to security implications.
The operational impact of this vulnerability extends beyond simple parsing errors, as it creates opportunities for request smuggling attacks that can bypass network security controls. When an attacker exploits this vulnerability, they can potentially manipulate HTTP requests in ways that confuse intermediaries such as proxies, load balancers, or firewalls. The attack vector becomes particularly dangerous in environments where HTTP traffic passes through multiple security layers, as the malformed chunked requests can cause inconsistent interpretation of the request boundaries. This behavior aligns with ATT&CK technique T1071.004, which covers application layer protocol manipulation, specifically targeting HTTP protocol handling to evade detection mechanisms.
The vulnerability's exploitation requires specific conditions to be effective, namely the use of the pure Python implementation of aiohttp or explicit disabling of C extensions through the AIOHTTP_NO_EXTENSIONS flag. This means that environments using the optimized C extensions are not affected by this particular vulnerability, as the native implementations correctly handle the chunk extension parsing. However, organizations that have explicitly disabled extensions for debugging or compatibility reasons may be vulnerable. The fix implemented in version 3.10.11 addresses the core parsing logic to ensure proper handling of newline characters within chunk extensions, maintaining the correct HTTP protocol compliance while preserving functionality.
Organizations should prioritize updating their aiohttp installations to version 3.10.11 or later to mitigate this vulnerability. System administrators should also review their deployment configurations to ensure that C extensions are properly enabled unless there are specific operational requirements for the pure Python implementation. Security monitoring should include detection of anomalous HTTP chunked transfer encoding patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of thorough protocol compliance testing, particularly in security-critical components where parsing errors can have far-reaching consequences beyond simple functional failures.