The HTTP parsers were vulnerable to a request smuggling attack relating to WebSocket upgrades.
If using the server-side component, it may be possible for an attacker to execute a request smuggling vulnerability using an edge case in the WebSocket upgrade procedure. AIOHTT is unaware of any public exploit code.
Patch: https://github.com/aio-libs/aiohttp/commit/6ae358f0983c3f4d6f67692b2f8e65dc8e091c98