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Fuzzing Rust

Fuzzing Rust Code — cargo-fuzz, libFuzzer, AFL.rs at Scale

Rust's memory safety doesn't cover logic bugs, panics, or unsafe blocks. Fuzze.rs runs continuous libFuzzer and AFL++ campaigns against your crates with zero infrastructure work.

Rust catches a huge class of memory-safety bugs at compile time — but fuzzing remains the highest-yield way to find the bugs the borrow checker can't see. Panics on attacker-controlled input, logic bugs in parsers and state machines, and the genuine vulnerabilities hiding inside `unsafe` blocks are exactly what coverage-guided fuzzing surfaces fastest.

Fuzze.rs runs libFuzzer (via cargo-fuzz) and AFL++ (via afl.rs) as managed campaigns against your Rust targets. Push a Dockerfile, point us at your fuzz target, and crashes start landing in the dashboard within hours.

Why it matters

Catches panics on attacker-controlled input

Rust's `unwrap()` and array-index panics are denial-of-service primitives in any server handling user data. cargo-fuzz finds them fast.

Audits every `unsafe` block

Memory-safety bugs in `unsafe` blocks fuzz exactly like C/C++. Coverage-guided campaigns reach paths your unit tests don't.

Validates parsers, codecs, and protocols

The classic libFuzzer wheelhouse. Anything that takes a `&[u8]` and produces structured output is a natural target.

Runs continuously, not just on PR

Real Rust bugs surface after millions of executions. Continuous campaigns find what one-shot CI runs miss.

Workflow

  1. 1

    Write a libFuzzer harness

    Use cargo-fuzz init / cargo-fuzz add target_name to scaffold a #[fuzz_target] entry point that consumes &[u8].

  2. 2

    Build the Docker image

    Standard rust:slim base + cargo install cargo-fuzz. We supply a starter Dockerfile in the docs.

  3. 3

    Push and start a job

    Either via the Fuzze.rs dashboard or POST /api/jobs/start. Optional seed corpus uploaded alongside.

  4. 4

    Watch coverage climb

    Branch coverage and execs/sec stream live. Most crates plateau in 6-24 hours.

  5. 5

    Triage crashes

    Stack-trace-based deduplication. Minimised reproducers downloadable per crash.

  6. 6

    Wire into CI

    POST a short fuzz run from your CI pipeline on every PR; a failing crash blocks merge.

Fuzzers we’d pick

  • libFuzzer (via cargo-fuzz) — the default for Rust. Tight feedback loop, fast iteration, in-process.
  • AFL++ (via afl.rs) — strong on stateful targets and where libFuzzer's persistent-mode constraints hurt.
  • Power Fuzzing — run both engines against the same target in parallel for broader coverage.
Start fuzzing your Rust crates →

First month 50% off. Cancel anytime.