CVE-2023-49082 is a vulnerability classified under CWE-93 (Improper Neutralization of CRLF Sequences) and CWE-20 (Improper Input Validation) affecting aiohttp, a widely used asynchronous HTTP client/server framework for Python's asyncio. The vulnerability stems from insufficient validation of the HTTP method and version fields in incoming requests, which allows an attacker who can control the HTTP method to inject CRLF sequences. This injection enables the attacker to modify HTTP requests by inserting new headers or even crafting entirely new HTTP requests, a technique commonly referred to as HTTP request smuggling. The flaw is exploitable without authentication or user interaction, provided the attacker can influence the HTTP method of the request. If the attacker can also control the HTTP version, the risk of request smuggling increases, potentially bypassing security controls or causing misrouting of requests. The vulnerability affects aiohttp versions earlier than 3.9.0, where the issue has been addressed. The CVSS v3.1 base score is 5.3 (medium severity), reflecting network attack vector, low attack complexity, no privileges required, no user interaction, unchanged scope, no confidentiality impact, limited integrity impact, and no availability impact. No known exploits have been reported in the wild to date. This vulnerability is particularly relevant for web applications and APIs built on aiohttp that accept HTTP requests with attacker-controlled methods, which could be leveraged to manipulate HTTP traffic and potentially bypass security mechanisms or inject malicious headers.

For European organizations, the impact of CVE-2023-49082 depends largely on the extent to which aiohttp is used in their web infrastructure, especially in public-facing APIs and services. Successful exploitation could allow attackers to manipulate HTTP requests, potentially bypassing security controls such as web application firewalls, authentication mechanisms, or caching layers. This could lead to integrity issues, such as unauthorized header injection, session fixation, or request smuggling attacks that confuse backend systems or proxies. While confidentiality and availability impacts are not directly indicated, the manipulation of HTTP requests could facilitate further attacks or data leakage indirectly. Organizations relying on aiohttp in critical services may face increased risk of targeted attacks, especially if attackers can control HTTP methods in requests (e.g., via proxy or client-side manipulation). Given the medium severity and no requirement for authentication, the vulnerability poses a moderate risk that should be addressed promptly to avoid exploitation in complex attack chains.

1. Upgrade aiohttp to version 3.9.0 or later, where this vulnerability has been patched. 2. Implement strict input validation and sanitization on HTTP methods and headers at the application or proxy level to prevent injection of CRLF sequences. 3. Use web application firewalls (WAFs) configured to detect and block HTTP request smuggling and header injection attempts. 4. Monitor HTTP traffic for anomalous methods or malformed requests that could indicate exploitation attempts. 5. Limit the ability of external users to control HTTP methods where possible, for example by restricting allowed methods to a whitelist. 6. Conduct security testing and code reviews focusing on HTTP request handling in aiohttp-based applications. 7. Employ layered security controls such as reverse proxies or API gateways that can normalize and validate incoming requests before they reach aiohttp services. 8. Stay informed on updates from aio-libs and security advisories for any further patches or related vulnerabilities.