Its not about privileges, the iMessage blastdoor exploit built a turing machine using a weird old image format and then escaped.
https://googleprojectzero.blogspot.com/2021/12/a-deep-dive-i...
https://googleprojectzero.blogspot.com/2021/12/a-deep-dive-i...
From the conclusion of the second post, which analyses the sandbox escape:
> Perhaps the most striking takeaway is the depth of the attack surface reachable from what would hopefully be a fairly constrained sandbox. [...] The expressive power of NSXPC just seems fundamentally ill-suited for use across sandbox boundaries, even though it was designed with exactly that in mind. [...]
(The above is severely cut down, reading at least the entire conclusion or even the whole post is worth it)
https://googleprojectzero.blogspot.com/2022/03/forcedentry-s...