iOS does sandbox their processes really well, that's why this hack was as difficult as it was. The Safari thing you're talking about is JIT - iOS disables all runtime code generation across the system except in Safari (for JavaScript), but this is a completely separate thing from sandboxing.
Actually, no, I now remember this was about iMessage specifically and how it isn't completely isolated/runs as system service or sth? Or about the renderer?
Which would make sense because these attacks seem to exploit the same weakness.
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