Sounds like a "won't fix", too:

"So, yeah, I don't think there's anything to fix in systemd here."
- Poettering

Not sure what's more troubling here[1]; the lack of concern, the
digression from POSIX, or the bug/backdoor itself. Maybe all three.

useradd 0day works on Devuan. adduser 0day does not. Which is correct?

[1] https://github.com/systemd/systemd/issues/6237