See how websockets project compares to other vendors in security performance
aaugustin websockets version 4 contains a CWE-409: Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in Servers and clients, unless configured with compression=None that can result in Denial of Service by memory exhaustion. This attack appear to be exploitable via Sending a specially crafted frame on an established connection. This vulnerability appears to have been fixed in 5.
The aaugustin websockets library before 9.1 for Python has an Observable Timing Discrepancy on servers when HTTP Basic Authentication is enabled with basicauthprotocolfactory(credentials=...). An attacker may be able to guess a password via a timing attack.