They do keep runtime array indexing checks on. I'm pretty sure I remember reading a comment from Steve Klabnik on here that they only turned off overflow checks

They do keep runtime array indexing checks on. I'm pretty sure I remember reading a comment from Steve Klabnik on here that they only turned off overflow checks in release builds by default because array range checks stay on. With neither over/underflow checking nor array index checks, it's a lot more likely you'd accidentally use an out-of-bounds index. For example, there was an iMessage vulnerability a while ago that relied on unsigned overflow to create an undersized buffer so that data would be written out of bounds later [0]. If it had been written in Rust (or Ada), with overflow checking on, it would have panicked upon overflow, and with it off, it would have panicked when using an out-of-bounds index. With both off, you get this vulnerability. [0]: https://googleprojectzero.blogspot.com/2021/12/a-deep-dive-into-nso-zero-click.html https://googleprojectzero.blogspot.com/2021/12/a-deep-dive-i...