"OpenSSH, the most popular sshd implementation, doesn't link the liblzma library, but Debian and many other Linux distributions add a patch to link sshd to systemd, a program that loads a variety of services during the system bootup. Systemd, in turn, links to liblzma, and this allows xz Utils to exert control over sshd."
Compare with:
"Xz is an open-source compression program, as well as a library that can be used to help you write your own program that deals with compressed data. It is used by a fairly large number of other programs, one of which is OpenSSH."
https://news.ycombinator.com/item?id=39881049
GNU's binutils links to liblzma. binutils is even more ubiquitous than OpenSSH; in most cases it's probably used in the compilation of OpenSSH, the operating systems on which sshd runs, and so on. The bad guys certainly picked a good project to potentially get deep into open source software.