Any user process can append anything they want to your shell rc (.bashrc, .zshrc). In this case, they added a bash function for a fake sudo prompt. It then uses the password the user entered to run a malicious payload as root.
The freaking point is that basically anything worth running will have that amount of access, even Flatpaks. And you don't freaking know what's malicious before hand.
I think that depends on your point of view. I wouldn't run a program on my computer unless I were sure that it's not malicious. And if you mean that some program I already trust could be exploited, that's true even for the Linux kernel or any sandbox / security solution you would come up with. I'm not denying that there's always a risk, but there's nothing good in running arbitrary code that you can't trust.
It’s not, but the grandparent does point out 1 major flaw with sudo being a typically command that goes through normal path discovery. It makes it easier to escalate from a compromised user account to a compromised root account, since the end user is likely to type the root password into a command that can be shadowed in their user space.
You do realize you can do the exact same thing on macOS? Just alias sudo to whatever you want. BSD I assume you can do the same with doas.
No desktop system is safe from your attack, unless you take specific precautions like chattr on the file or chmodding your home directory, but that can lead to weird breakage.
