I don't think this is a problem with proc macros or package managers. This is just a regular supply chain attack, no?

The way I understand it, sandboxing would be detrimental to code performance. Imagine coding a messaging system with a serve struct, only for serde code to be much slower due to sandboxing. For release version it could be suggested to disable sandboxingy but then we would have gained practically nothing.

In security terms, being prepared for incidents is most often better than trying to prevent them. I think this applies here too, and cargo helps here. It can automatically update your packages, which can be used to patch attacks like this out.

If you think I'm wrong, please don't hesitate to tell me!