Comment by mpyne

Well, OpenSSH contributes to this by mixing hashes from the shadow file. The musl code would be correct if OpenSSH passed in the hash from the user account that is being logged-in.

They instead pass in a different user’s hash (to avoid timing attacks) but end up comparing the result from musl against the actual user account, defeating musl’s simplistic safeguard to avoid this very issue.

I’d probably still call this a musl thing. Errors should result in a NULL return even if the application crashes from there, but at the very least a return value intended to not match any actual hash in /etc/shadow should be a random string or predefined UUID or something other than *.