2nd/10_Wiki/Topics/Programming & Language/Fuzzing.md

---
id: wiki-2026-0508-fuzzing
title: Fuzzing
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Fuzz Testing, Coverage-Guided Fuzzing]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [security, testing, dast]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: C/Rust/Go
  framework: AFL++/libFuzzer/cargo-fuzz
---

# Fuzzing

## 매 한 줄
> **"매 random/mutated input 으로 crash, hang, UB 의 hunt"**. 매 1988 Miller (Wisconsin) 의 random input shell experiment 가 origin. 2026 현재 매 coverage-guided (AFL++, libFuzzer, Honggfuzz), structure-aware (libprotobuf-mutator), grammar-based (Nautilus), LLM-augmented (OSS-Fuzz Gen) 가 mainstream. Google OSS-Fuzz 가 100K+ bug 발견, Chrome/Linux kernel/OpenSSL 의 routine workflow.

## 매 핵심

### 매 fuzzing categories
- **Black-box (dumb)**: random input, no instrumentation. 매 zzuf, radamsa.
- **Coverage-guided (grey-box)**: input 의 mutation + branch coverage feedback. 매 AFL++, libFuzzer, Honggfuzz.
- **White-box (concolic)**: symbolic execution + solver. 매 KLEE, SAGE.
- **Structure-aware**: protobuf, JSON 의 grammar 의 valid input. 매 libprotobuf-mutator, FuzzGrammar.
- **Differential**: 매 동일 input 을 두 implementation 에 → divergence 의 bug.

### 매 sanitizers
- ASan (heap/stack OOB, UAF), UBSan (UB), MSan (uninit read), TSan (data race), LSan (leak).
- 매 fuzzing 의 corpus 는 sanitizer 와 함께 build 의 mandatory.

### 매 응용
1. Memory-safety bug discovery (C/C++ codebases).
2. Parser hardening (image, video, network protocols).
3. Browser engine (V8 fuzzilli, JSC fuzzer).
4. Crypto library (OpenSSL, BoringSSL via OSS-Fuzz).

## 💻 패턴

### libFuzzer (C++)
```cpp
// fuzz_target.cc — clang -fsanitize=fuzzer,address fuzz_target.cc parser.cc
#include <stdint.h>
#include <stddef.h>
#include "parser.h"

extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
  if (size < 4) return 0;
  Parser p;
  p.Parse(reinterpret_cast<const char*>(data), size);  // ASan catches OOB/UAF
  return 0;
}
```

### cargo-fuzz (Rust)
```rust
// fuzz/fuzz_targets/parse.rs
#![no_main]
use libfuzzer_sys::fuzz_target;

fuzz_target!(|data: &[u8]| {
    if let Ok(s) = std::str::from_utf8(data) {
        let _ = mycrate::parse(s);  // panics 는 fuzz crash 로 catch
    }
});
```
```bash
cargo fuzz run parse -- -max_total_time=600
```

### Go native fuzzing (1.18+)
```go
func FuzzParseURL(f *testing.F) {
    f.Add("http://example.com")
    f.Fuzz(func(t *testing.T, s string) {
        u, err := url.Parse(s)
        if err == nil && u.String() != s && url.QueryEscape(u.String()) == "" {
            t.Errorf("roundtrip mismatch: %q", s)
        }
    })
}
```
```bash
go test -fuzz=FuzzParseURL -fuzztime=10m
```

### AFL++ (compile-time instrumentation)
```bash
CC=afl-clang-fast CXX=afl-clang-fast++ ./configure
make -j8
mkdir in; echo "seed" > in/0
afl-fuzz -i in -o out -- ./target @@
```

### Structure-aware (libprotobuf-mutator)
```cpp
DEFINE_PROTO_FUZZER(const my::Message& msg) {
  HandleMessage(msg);  // valid proto guaranteed → deeper coverage
}
```

### OSS-Fuzz integration
```dockerfile
FROM gcr.io/oss-fuzz-base/base-builder
RUN apt-get install -y libssl-dev
COPY . $SRC/myproject
COPY build.sh $SRC/
WORKDIR $SRC/myproject
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| C/C++ memory bug hunt | libFuzzer + ASan/UBSan |
| Rust panic / logic bug | cargo-fuzz |
| Network protocol parser | AFL++ + structure-aware mutator |
| Two implementations comparison | Differential fuzzing |
| Continuous (open-source) | OSS-Fuzz |
| Grammar-rich (JS, SQL) | Grammar-based (Nautilus, fuzzilli) |

**기본값**: 매 coverage-guided (libFuzzer/AFL++) + ASan + corpus minimization + CI 에 5min smoke.

## 🔗 Graph
- 부모: [[DAST (동적 애플리케이션 보안 테스트)]]
- 변형: [[SCA (소프트웨어 구성 분석)]]
- 응용: [[OSS-Fuzz]] · [[V8 엔진 힙 아키텍처]]
- Adjacent: [[Property-Based Testing]]

## 🤖 LLM 활용
**언제**: 매 untrusted input 의 parser, codec, deserializer 가 있는 경우. 매 security-critical library 의 release 전 mandatory.
**언제 X**: pure functional code 의 deterministic 한 input space (property-based testing 이 더 적절). 매 GUI / network state-heavy code.

## ❌ 안티패턴
- **Sanitizer 없이 fuzz**: 매 silent corruption 을 miss. 매 ASan 의 mandatory.
- **Seed corpus 없음**: 매 coverage 의 plateau 가 빠름. 매 valid sample 10-100 개 의 seed.
- **CI 에 30s 만 fuzz**: 매 너무 짧음. 매 minimum 10min, ideal continuous (OSS-Fuzz pattern).
- **Crash 만 의 focus**: 매 hang, OOM, slow input 도 bug. 매 timeout / rss_limit 설정.

## 🧪 검증 / 중복
- Verified (Miller 1990 "Empirical Study of Reliability of UNIX Utilities"; AFL++ docs; OSS-Fuzz reports).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — coverage-guided + sanitizers + OSS-Fuzz |