Python -- Regular Expression DoS attack against client

Ben Caller and Matt Schwager reports:

Python 2.7 through 2.7.17, 3.5 through 3.5.9, 3.6 through 3.6.10, 3.7
through 3.7.6, and 3.8 through 3.8.1 allows an HTTP server to conduct
Regular Expression Denial of Service (ReDoS) attacks against a client
because of urllib.request.AbstractBasicAuthHandler catastrophic
backtracking.