On crates.io, a good heuristic is to look at two numbers: the number of dependents and the number of downloads. If both are high, it's _probably_ fine. Otherwise, I'll manually audit the code.
That's not a complete solution, especially not if you're worried about this from a security perspective, but it's a good approximation if you're worried about the general quality of your dependencies.
You can lump anything under "security" for particular use cases, but what's the point of words then.
Tokio on the other hand is the library whose maintainer decided to download a binary blob during build: https://github.com/tokio-rs/prost/issues/562 https://github.com/tokio-rs/prost/issues/575
Good luck catching such issues across dozens of crates.
All three modern C++ standard libraries are of course Free Software. They are respectively the GNU libstdc++, Clang's libc++ and the Microsoft STL. Because it's a huge sprawling library, you quickly leave the expertise of the paid maintainers and you're into code that some volunteer wrote for them and says it's good. Sounds like random third parties to me.
Now, I'm sure that Stephan T. Lavavej (the Microsoft employee who looks after the STL, yes, nominative determinism) is a smart and attentive maintainer, and so if you provide a contribution with a function named "_Upload_admin_creds_to_drop_box" he's not going to apply that but equally Stephen isn't inhumanly good, so subtle tricks might well get past him. Similar thoughts apply to the GNU and Clang maintainers who don't have funny names.
Having paid maintainers, code review, test suites, strict contribution guidelines, etc is state of the art for open source software that some transitive crate dependency can only dream to achieve.
With Rust, it’s literally a random third party.