Mainly memory safety; split (which is also used for other programs like sort) had a memory heap overflow issue last year to name one. The GNU Coreutils are well tested and very well written, the entire suite of programs has a CVE only once every few years from what I can see, but they do exist and most of those would be solved with a memory and type safe language.

That said, Rust also handles parallelism and concurrency much better than C ever could, though most of these programs don’t really benefit from that or not much since they already handled this quite well, especially for C programs.