The “socket” module provides a pure-Python fallback to the socket.socketpair() function for platforms that don’t support AFUNIX, such as Windows. This pure-Python implementation uses AFINET 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.