Integer overflow can happen in Rust, but it's well-defined, not undefined. This helps.

Bounds checking is part of indexing, and so even if an index overflows, the check should happen, and panic.

"impossible" is a strong word, but it would be significantly less likely in Rust. If you did the same thing as you did in C, with unsafe, then it could happen. But there's not a lot of reason to 99.9999% of the time, as it's the more difficult and less ergonomic option.