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cargo-fuzz is the de facto fuzzing tool for Rust projects using Cargo. Use for fuzzing Rust code with libFuzzer backend.
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</> SKILL.md
cargo-fuzz.SKILL.md
---name: cargo-fuzz
type: fuzzer
description: >
cargo-fuzz is the de facto fuzzing tool for Rust projects using Cargo.
Use for fuzzing Rust code with libFuzzer backend.
---# cargo-fuzz
cargo-fuzz is the de facto choice for fuzzing Rust projects when using Cargo. It uses libFuzzer as the backend and provides a convenient Cargo subcommand that automatically enables relevant compilation flags for your Rust project, including support for sanitizers like AddressSanitizer.
## When to Use
cargo-fuzz is currently the primary and most mature fuzzing solution for Rust projects using Cargo.
| Fuzzer | Best For | Complexity |
|--------|----------|------------|
| cargo-fuzz | Cargo-based Rust projects, quick setup | Low |
| AFL++ | Multi-core fuzzing, non-Cargo projects | Medium |
| LibAFL | Custom fuzzers, research, advanced use cases | High |
**Choose cargo-fuzz when:**
- Your project uses Cargo (required)
- You want simple, quick setup with minimal configuration
- You need integrated sanitizer support
- You're fuzzing Rust code with or without unsafe blocks
## Quick Start
```rust
#![no_main]
> **See Also:** For detailed coverage analysis techniques and systematic coverage improvement,
> see the **coverage-analysis** technique skill.
## Advanced Usage
### Tips and Tricks
| Tip | Why It Helps |
|-----|--------------|
| Start with a seed corpus | Dramatically speeds up initial coverage discovery |
| Use `--sanitizer none` for safe Rust | 2x performance improvement |
| Check coverage regularly | Identifies gaps in harness or seed corpus |
| Use dictionaries for parsers | Helps overcome magic value checks |
| Structure code as library | Required for cargo-fuzz integration |
### libFuzzer Options
Pass options to libFuzzer after `--`:
```bash
# See all options
cargo +nightly fuzz run fuzz_target_1 -- -help=1
# Set timeout per run
cargo +nightly fuzz run fuzz_target_1 -- -timeout=10
# Use dictionary
cargo +nightly fuzz run fuzz_target_1 -- -dict=dict.dict
# Limit maximum input size
cargo +nightly fuzz run fuzz_target_1 -- -max_len=1024
```
### Multi-Core Fuzzing
```bash
# Experimental forking support (not recommended)
cargo +nightly fuzz run --jobs 1 fuzz_target_1
```
Note: The multi-core fuzzing feature is experimental and not recommended. For parallel fuzzing, consider running multiple instances manually or using AFL++.
## Real-World Examples
### Example: ogg Crate
The [ogg crate](https://github.com/RustAudio/ogg) parses Ogg media container files. Parsers are excellent fuzzing targets because they handle untrusted data.
```bash
# Clone and initialize
git clone https://github.com/RustAudio/ogg.git
cd ogg/
cargo fuzz init
```
Harness at `fuzz/fuzz_targets/fuzz_target_1.rs`:
```rust
#![no_main]
use ogg::{PacketReader, PacketWriter};
use ogg::writing::PacketWriteEndInfo;
use std::io::Cursor;
use libfuzzer_sys::fuzz_target;
fn harness(data: &[u8]) {
let mut pck_rdr = PacketReader::new(Cursor::new(data.to_vec()));
pck_rdr.delete_unread_packets();
let output = Vec::new();
let mut pck_wtr = PacketWriter::new(Cursor::new(output));
