CVE-2023-47641 is a vulnerability classified under CWE-444 (Inconsistent Interpretation of HTTP Requests), commonly known as HTTP Request/Response Smuggling, affecting aiohttp, an asynchronous HTTP client/server framework for Python's asyncio. The flaw occurs when both Content-Length (CL) and Transfer-Encoding (TE) headers are present in an HTTP/1.1 request. According to HTTP/1.1 specifications, if both headers exist, the Transfer-Encoding header should take precedence. However, inconsistent parsing between a frontend reverse proxy and the aiohttp backend can lead to different interpretations of the request body length. Specifically, if the frontend proxy ignores a malformed TE header (e.g., 'chunked123') and processes the CL header, while aiohttp backend treats the request as chunked due to the presence of any TE header, this mismatch allows an attacker to smuggle requests. This can poison the backend connection, enabling the attacker to bypass proxy security rules, inject malicious headers such as authentication tokens, or manipulate subsequent requests. If combined with an open redirect vulnerability, attackers could redirect users to malicious sites and log their requests. The vulnerability requires no prior authentication but does require user interaction to send crafted HTTP requests. The issue was addressed in aiohttp version 3.8.0 by correcting the header parsing logic to align with HTTP standards. There are no known workarounds, and no exploits have been observed in the wild as of the publication date (November 14, 2023). The CVSS v3.1 base score is 3.4 (low), reflecting the limited impact and higher complexity due to required conditions and user interaction.

For European organizations, the primary impact of CVE-2023-47641 lies in the potential bypass of proxy security controls and the poisoning of backend connections in aiohttp-based services. This can lead to unauthorized header injection, such as authentication tokens, potentially allowing attackers to impersonate users or escalate privileges within internal applications. Additionally, when combined with open redirect vulnerabilities, attackers could redirect users to malicious websites and capture sensitive request data, impacting user privacy and confidentiality. The vulnerability does not directly affect data integrity or availability but compromises confidentiality in specific deployment scenarios involving reverse proxies and aiohttp backends. Organizations relying on aiohttp for asynchronous HTTP services, especially those exposing APIs or web services behind reverse proxies, are at risk. The lack of known exploits reduces immediate threat but does not eliminate the risk of future attacks. Given the widespread use of Python and aiohttp in web applications and microservices across Europe, especially in sectors like finance, healthcare, and government, exploitation could lead to data leakage and unauthorized access, undermining trust and compliance with data protection regulations such as GDPR.

The primary mitigation is to upgrade all aiohttp instances to version 3.8.0 or later, where the vulnerability has been fixed. Since no known workarounds exist, patching is critical. Organizations should audit their infrastructure to identify aiohttp usage, particularly in backend services behind reverse proxies that accept both Content-Length and Transfer-Encoding headers. Configuration hardening of reverse proxies to reject or normalize requests containing both headers can reduce risk. Implement strict input validation and header sanitization at the proxy level to prevent malformed TE headers. Monitoring and logging HTTP request anomalies can help detect attempts to exploit request smuggling. Additionally, review and remediate any open redirect vulnerabilities that could be chained with this issue. Employing Web Application Firewalls (WAFs) with updated signatures to detect request smuggling attempts may provide additional protection. Finally, conduct security testing, including fuzzing and penetration testing, focusing on HTTP header parsing inconsistencies in the affected environments.