there's a hypothetical compiler exploit that i always thought was a bit out there but it was a big deal with some folks, and i haven't heard anyone talk about it in a hot minute. the gist is, you make a custom version of clang or whatever that adds a payload into what it builds (presumably not everything or it would be easy to track down) including itself such that it is self-perpetuating, and then you somehow trick the clang maintainers into shipping that instead of a real release build etc