Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
aiohttp is an asynchronous HTTP client/server framework for asyncio and Python. The HTTP parser in AIOHTTP has numerous problems with header parsing, which could lead to request smuggling. This parser is only used when "AIOHTTP_NO_EXTENSIONS" is enabled (or not using a prebuilt wheel). This issue affects the versions through to 3.8.5 and 4.0.0a0 through 4.0.0a1
CWE-444 - HTTP Request Smuggling
Entities such as web servers, web caching proxies, and application firewalls could parse HTTP requests differently. When there are two or more such entities in the path of an HTTP request, an attacker can send a specially crafted HTTP request that is seen as two different sets of requests by the attacked devices, allowing the attacker to smuggle a request into one device without the other device being aware of it. Such a vulnerability can prove devastating, for it enables further attacks on the application, like web cache poisoning, session hijacking, cross-site scripting, security bypassing, and sensitive information exposure.