And even if you could fix all of rustc's soundness holes, or otherwise prevent user code from exploiting them, a soundness bug in any third-party library can also make it possible for malicious crates to trigger arbitrary behavior from safe code.
[...]
This is why we need to emphasize that while Rust's static analyses are very good at limiting accidental vulnerabilties in non-malicious code, they are not a sandbox system that can place meaningful limits on malicious code.
mbrubeck in Regarding the Security / Safety of Libraries on Crates.io