In my last post I talked about a way I found to execute arbitrary code in Unity using no custom scripts, only built-in components. This allowed potential attacks against Unity games that load AssetBundles from untrusted sources since, although AssetBundles can’t include custom scripts, they can include GameObjects containing these built-in components. The attack I outlined in that blog used UnityEvents, which are primarily exposed via Unity’s built-in UI elements, but the attack required user interaction to trigger.
In this post I am going to discuss a zero-click method of triggering UnityEvents, along with some additional things I’ve learned on this topic. I will also introduce a new exploit that does not use UnityEvents and removes one of the limitations of the UnityEvent-based attack (while adding limitations of its own). Finally, I will give some updated remediation thoughts.