fuzzing-dictionary

SKILL.md

Domain-specific token guidance for fuzzers targeting parsers, protocols, and file formats.

Provides dictionary file format with quoted strings, hex escapes, and key-value pairs that guide fuzzer mutations toward meaningful inputs and deeper code paths

Works cross-fuzzer with libFuzzer, AFL++, and cargo-fuzz via standard command-line flags (-dict=, -x)

Includes generation methods: LLM prompts, extraction from headers and binaries, and AFL++ auto-dictionary via compile-time string comparison analysis

Covers common patterns for protocol keywords, magic bytes, and configuration file tokens with anti-patterns to avoid (oversized dictionaries, missing escapes, duplicates)

Fuzzing Dictionary

A fuzzing dictionary provides domain-specific tokens to guide the fuzzer toward interesting inputs. Instead of purely random mutations, the fuzzer incorporates known keywords, magic numbers, protocol commands, and format-specific strings that are more likely to reach deeper code paths in parsers, protocol handlers, and file format processors.

Overview

Dictionaries are text files containing quoted strings that represent meaningful tokens for your target. They help fuzzers bypass early validation checks and explore code paths that would be difficult to reach through blind mutation alone.

Key Concepts

Concept
Description

Dictionary Entry
A quoted string (e.g., "keyword") or key-value pair (e.g., kw="value")

Hex Escapes
Byte sequences like "\xF7\xF8" for non-printable characters

Token Injection
Fuzzer inserts dictionary entries into generated inputs

Cross-Fuzzer Format
Dictionary files work with libFuzzer, AFL++, and cargo-fuzz

When to Apply