I take it that "server" in this context includes the remote party in a "serverless" transfer. I mean, I take it this isn't particular to the rsync daemon.
It sounds like a very serious defect, very easy to exploit. It needed to be addressed quickly. I'm not surprised they skipped the code review.
Exactly. I'm usually worried about the opposite scenario (the client infecting the server). If you're copying files from a personal computer it might have all sorts of random software running on it that's accumulated over the years. Whereas on a remote server you tend to have a better security posture, and aren't installing random software and apps. Admittedly, that might just be my personal use case though.
It sounds like a very serious defect, very easy to exploit. It needed to be addressed quickly. I'm not surprised they skipped the code review.