fuzzing-input-generator

Fuzzing Input Generator

Overview

Generate comprehensive fuzz testing inputs to uncover bugs, crashes, and security vulnerabilities by systematically testing functions with edge cases, invalid inputs, and randomized data.

Workflow

1. Analyze the Target Function

Understand what needs to be fuzzed:

Identify input types:

• Strings (text, paths, URLs, etc.)
• Numbers (integers, floats)
• Booleans
• Collections (lists, dicts, sets)
• Structured data (JSON, XML)
• Files or binary data
• Combinations of above

Understand expected behavior:

• What are valid inputs?
• What should happen with invalid inputs?
• Are there documented constraints?
• What error handling exists?

Extract function signature:

def process_user_input(name: str, age: int, email: str) -> dict:
    """Process user registration data."""
    # Analyze: expects string, int, string
    # Constraints: name non-empty, age > 0, email format

2. Select Fuzzing Strategy

Choose appropriate fuzzing approaches:

Edge Case Fuzzing

Test boundary conditions and special values:

• Empty inputs
• Very large inputs
• Minimum/maximum values
• Zero, negative numbers
• Special characters
• Null/None values

Invalid Input Fuzzing

Test with malformed or incorrect data:

• Wrong types
• Invalid formats
• Out-of-range values
• Malformed structures
• Encoding issues

Random Valid Fuzzing

Generate random but technically valid inputs:

• Random strings of various lengths
• Random numbers in valid ranges
• Random but well-formed structures
• Valid but unusual combinations

Security Fuzzing

Test for vulnerabilities:

• Injection attacks (SQL, command, XSS)
• Path traversal
• Buffer overflows
• Format string attacks
• Unicode exploits

3. Generate Fuzz Test Code

Create Python test functions with fuzzing inputs.

Basic Template

import pytest
import random
import string

def fuzz_<function_name>():
    """Fuzz test for <function_name>."""

    # Edge cases
    edge_cases = [
        # Add specific edge case inputs
    ]

    # Invalid inputs
    invalid_inputs = [
        # Add invalid inputs
    ]

    # Random valid inputs
    def generate_random_valid():
        # Generate random but valid input
        pass

    # Test edge cases
    for input_data in edge_cases:
        try:
            result = function_under_test(input_data)
            # Check result or at least that it doesn't crash
        except Exception as e:
            # Document or assert expected exceptions
            pass

    # Test invalid inputs
    for input_data in invalid_inputs:
        # Similar testing pattern
        pass

    # Test random inputs
    for _ in range(100):
        random_input = generate_random_valid()
        # Test with random input