Vibe codingHardvc-g025

Subject Ai code reviewLevel Senior–Staff~18 minCommon in Security interviewsIndustries Software development, Technology

Question

An AI agent wrote this Rust function to generate a session token, using a method on the rand crate it claimed produces 'cryptographically secure' bytes. It compiles after the AI adjusted the import. Review it for a production auth system.

rust

1use rand::Rng;2 3fn new_session_token() -> String {4    let mut rng = rand::thread_rng();5    let token: String = (0..16)6        .map(|_| {7            let c = rng.gen_range(b'a'..=b'z') as char;8            c9        })10        .collect();11    token12}

What a strong answer looks like

Treat the AI’s output as a draft to verify, not an answer to trust. Name the specific flaw and the input that triggers it, say how you’d catch it — tests, edge cases, reading critically — and how you’d re-prompt or decompose to get it right.

Learn the concepts

Describe your solution

Vibe coding: describe the solution in plain language (or narrate it) and the coach grades your approach. Generating runnable code from your description is coming next.

Run or narrate your approach, then ask the coach.