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Configuration File Loader

The MCP Fuzzer includes a powerful configuration file loader that allows you to define all your fuzzing settings in YAML files, eliminating the need to pass numerous command-line parameters.

Overview

The configuration loader automatically discovers and loads configuration files from standard locations, supporting:

  • YAML format (.yml or .yaml files)
  • Automatic discovery from multiple locations
  • Environment variable overrides
  • Custom transport definitions
  • Authentication provider configurations
  • Safety and output settings

Configuration File Discovery

The loader searches for configuration files in the following order:

  1. Explicit path (if --config parameter is provided)
  2. Current directory: ./mcp-fuzzer.yml or ./mcp-fuzzer.yaml
  3. User config directory: ~/.config/mcp-fuzzer/mcp-fuzzer.yml

Basic Configuration Example

# mcp-fuzzer.yaml
# General settings
timeout: 30.0
log_level: "INFO"
safety_enabled: true

# Transport settings
http_timeout: 30.0
sse_timeout: 30.0
stdio_timeout: 30.0

# Fuzzing settings
mode: "both"
phase: "aggressive"
protocol: "http"
endpoint: "http://localhost:8000/mcp/"
runs: 10
runs_per_type: 5
max_concurrency: 5

Using Configuration Files

Command Line Usage

# Use default config file discovery
mcp-fuzzer

# Specify explicit config file
mcp-fuzzer --config /path/to/my-config.yaml

# Override config with command line (command line takes precedence)
mcp-fuzzer --config config.yaml --runs 20

Automatic Loading

When you run mcp-fuzzer without any parameters, it automatically:

  1. Searches for mcp-fuzzer.yml or mcp-fuzzer.yaml in current directory
  2. Falls back to ~/.config/mcp-fuzzer/mcp-fuzzer.yml
  3. Loads and applies the configuration
  4. Uses any remaining command-line arguments as overrides

Configuration Sections

Core Settings

# Basic fuzzing parameters
timeout: 30.0                    # Default timeout in seconds
tool_timeout: 30.0              # Tool-specific timeout
log_level: "INFO"               # DEBUG, INFO, WARNING, ERROR, CRITICAL
safety_enabled: true            # Enable safety features
fs_root: "~/.mcp_fuzzer"        # Root directory for file operations

# Transport-specific timeouts
http_timeout: 30.0
sse_timeout: 30.0
stdio_timeout: 30.0

Fuzzing Configuration

# Fuzzing behavior
mode: "tools"                   # tools, protocol, both
phase: "aggressive"             # realistic, aggressive, both
protocol: "http"                # http, https, sse, stdio, streamablehttp
endpoint: "http://localhost:8000"
runs: 10                        # Number of fuzzing runs
runs_per_type: 5               # Runs per protocol type
protocol_type: "InitializeRequest"  # Specific protocol type to fuzz
max_concurrency: 5              # Maximum concurrent operations

Safety Configuration

safety:
  enabled: true
  no_network: false              # Disable network access
  local_hosts:                   # Allowed hosts for network operations
    - "localhost"
    - "127.0.0.1"
    - "::1"
  header_denylist:               # Headers to block
    - "authorization"
    - "cookie"
  proxy_env_denylist:            # Proxy environment variables to strip
    - "HTTP_PROXY"
    - "HTTPS_PROXY"
  env_allowlist: []              # Environment variables to allow

Authentication Configuration

auth:
  providers:
    - type: "api_key"
      id: "openai_api"
      config:
        key: "sk-your-openai-api-key"
        header_name: "Authorization"
    - type: "basic"
      id: "secure_api"
      config:
        username: "user"
        password: "password"
    - type: "oauth"
      id: "github_api"
      config:
        token: "ghp-your-github-token"
        header_name: "Authorization"

  mappings:
    "chat_completion": "openai_api"
    "github_search": "github_api"
    "secure_tool": "secure_api"

Custom Transport Configuration

custom_transports:
  my_websocket_transport:
    module: "my_transports.websocket"
    class: "WebSocketTransport"
    description: "Custom WebSocket transport for real-time communication"
    factory: "my_transports.create_websocket_transport"
    config_schema:
      type: "object"
      properties:
        url:
          type: "string"
          description: "WebSocket URL"
        timeout:
          type: "number"
          default: 30.0

  grpc_transport:
    module: "my_transports.grpc"
    class: "GRPCTransport"
    description: "gRPC transport for high-performance communication"

Output Configuration

output:
  format: "json"                 # json, yaml, csv, xml
  directory: "./reports"         # Output directory
  compress: true                 # Compress output files
  types:                         # Specific output types
    - "fuzzing_results"
    - "error_report"
    - "safety_summary"
    - "performance_metrics"
  retention:
    days: 30                     # Retain files for N days
    max_size: "1GB"              # Maximum directory size

Advanced Examples

Development Environment

# development.yaml
timeout: 60.0
log_level: "DEBUG"
safety_enabled: false
mode: "tools"
phase: "realistic"
protocol: "stdio"
endpoint: "python test_server.py"
runs: 5
max_concurrency: 2

safety:
  enabled: false
  no_network: true

Production Testing

# production.yaml
timeout: 30.0
log_level: "WARNING"
safety_enabled: true
mode: "both"
phase: "aggressive"
protocol: "https"
endpoint: "https://api.production.com/mcp/"
runs: 50
max_concurrency: 10

safety:
  enabled: true
  no_network: false
  local_hosts: []
  header_denylist:
    - "authorization"
    - "cookie"
    - "x-api-key"

output:
  directory: "/var/log/mcp-fuzzer"
  compress: true
  retention:
    days: 90
    max_size: "10GB"

CI/CD Pipeline

# ci.yaml
timeout: 45.0
log_level: "INFO"
safety_enabled: true
mode: "tools"
phase: "realistic"
protocol: "http"
endpoint: "http://test-server:8000"
runs: 25
max_concurrency: 5

output:
  format: "json"
  directory: "./test-results"
  types:
    - "fuzzing_results"
    - "error_report"
    - "safety_summary"

Environment Variable Overrides

You can override configuration values using environment variables:

# Override specific values
export MCP_FUZZER_TIMEOUT=60.0
export MCP_FUZZER_LOG_LEVEL=DEBUG
export MCP_FUZZER_SAFETY_ENABLED=false

# Run with config file + environment overrides
mcp-fuzzer --config production.yaml

Configuration Validation

The configuration loader includes built-in validation:

  • Schema validation against JSON Schema
  • Type checking for all configuration values
  • Path validation for file and directory paths
  • URL validation for endpoints
  • Custom transport validation for module/class existence

Error Handling

The loader provides detailed error messages for common issues:

  • File not found: Clear indication of search paths tried
  • YAML parsing errors: Line numbers and context for syntax errors
  • Validation errors: Specific field and constraint violations
  • Import errors: Missing modules or classes for custom transports

Best Practices

Organization

  1. Use different configs for different environments:
  2. development.yaml - Relaxed settings for local development
  3. staging.yaml - Production-like settings for testing

  4. production.yaml - Strict settings for production systems

  5. Keep sensitive data separate:

  6. Use environment variables for API keys and passwords
  7. Store config files with restricted permissions
  8. Use secret management systems in production

Version Control

  1. Commit base configurations without sensitive data
  2. Use environment-specific overrides for production values
  3. Document configuration options in comments
  4. Version configuration files with your application

Security

  1. Restrict file permissions on configuration files
  2. Use environment variables for sensitive values
  3. Validate configuration before use
  4. Audit configuration changes in production

Migration from Command Line

Before (Command Line)

mcp-fuzzer \
  --mode tools \
  --protocol http \
  --endpoint http://localhost:8000 \
  --runs 10 \
  --phase aggressive \
  --timeout 30 \
  --log-level INFO \
  --enable-safety-system \
  --max-concurrency 5 \
  --output-dir ./reports

After (Configuration File)

# config.yaml
mode: "tools"
protocol: "http"
endpoint: "http://localhost:8000"
runs: 10
phase: "aggressive"
timeout: 30.0
log_level: "INFO"
safety_enabled: true
max_concurrency: 5

output:
  directory: "./reports"

# Simple command
mcp-fuzzer --config config.yaml

Troubleshooting

Common Issues

  1. Configuration not loading:
  2. Check file permissions
  3. Verify YAML syntax

  4. Ensure correct file extension (.yml or .yaml)

  5. Settings not applied:

  6. Command-line arguments override config file values
  7. Check environment variable precedence

  8. Verify configuration schema compliance

  9. Custom transport errors:

  10. Ensure module is in Python path
  11. Verify class exists and inherits from TransportProtocol
  12. Check factory function signature

Debug Mode

Enable debug logging to troubleshoot configuration issues:

export MCP_FUZZER_LOG_LEVEL=DEBUG
mcp-fuzzer --config your-config.yaml

This will show detailed information about: - Configuration file discovery - Loading process - Validation results - Applied settings