Local MITM of client-side X11 forwarding via abstract UNIX socket
pre-binding, scoped by upstream to Red Hat Enterprise Linux OpenSSH
clients. The vulnerable abstract-socket-first behavior is introduced
by Red Hat's downstream openssh-7.2p2-x11.patch, which Debian does not
carry: in the Debian openssh sources connect_local_xsocket() only
connects to the filesystem-path X socket, and no debian/patches entry
touches this code, so the vulnerable code path is not present. Debian
rates it undetermined.