AUR “packages” are just a recipe file that runs some commands that sources packages from somewhere else and builds them then puts them in the format required by the AUR package manager.

Normally it’s a source tarball downloaded directly from the project’s Git repo. But it can also fetch and install a binary package (for closed source software). Or it can install Node modules, or Python modules etc.

Point is, you can’t inject a script directly in AUR itself. You could add the malicious code directly to the recipe file but it would be obvious. You could also download a zip with the malware directly, but it would also be obvious.

So what they do is add the malware to modules published on another platform, and they’re downloaded indirectly, as a dependency of the Nth grade.

It’s very hard to detect, you can’t really notice this kind of attack with a glance at the recipe.

Here’s the AUR recipe (PKGBUILD file) for a random package:

https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=nautilus-git

This is a standard format for the recipe. It’s Bash code used to define variables and functions.

You’ll notice there’s no place to sneak in a Python script. There is some brief Bash code in the functions but any major stuff would stand out immediately. So would an command that fetches a malware zip from a weird URL.

Meanwhile, if you add node or python to the dependencies, and then run a command that installs a perfectly legit npm or pip module, nobody would bat an eye. It’s impossible to figure out that among the many upstream dependencies of that module there might be one that was subverted to discreetly run malware.

AUR is a very bad idea tbh and should not be used by the faint of heart. It makes it entirely too easy to pull this kind of crap.