I'm not sure, what they mean with those ratings, to be honest.

This whole article is about the yaml-rust library having been marked as unmaintained in the RUSTSEC advisory database: https://rustsec.org/packages/yaml-rust.html

RUSTSEC is not intrinsic to the language, but it's maintained by the Rust Foundation and there's some really solid tooling, which can tell you in the blink of an eye that one of your dependencies is insecure.

Well, and then there's some unofficial projects which curate libraries, like https://awesome-rust.com and https://lib.rs (the latter also serves as an alternative frontend for the official package registry https://crates.io ).