Pure-Python fallback of socket.socketpair() doesn’t authenticate peer connection

The
“socket” module provides a pure-Python fallback to the
socket.socketpair() function for platforms that don’t support AF_UNIX,
such as Windows. This pure-Python implementation uses AF_INET or
AF_INET6 to create a local connected pair of sockets. The connection
between the two sockets was not verified before passing the two sockets
back to the user, which leaves the server socket vulnerable to a
connection race from a malicious local peer.

Platforms that support AF_UNIX such as Linux and macOS are not affected by this vulnerability. Versions prior to CPython 3.5 are not affected due to the vulnerable API not being included.