[Plugin] Create File Type Allowlist Plugin using Plugin Framework

[crivetimihai]

Overview

Create a File Type Allowlist Plugin that restricts resource access to only configured file types and MIME types for enhanced security.

Plugin Requirements

Plugin Details

• Name: FileTypeAllowlistPlugin
• Type: Self-contained (native) plugin
• File Location: plugins/file_type_allowlist/
• Complexity: Low-Medium

Functionality

• Filter resources by MIME type and file extension
• Configurable allowlist for permitted file types
• Block access to potentially dangerous file types
• Support for MIME type detection and validation
• Custom error messages for blocked file types

Hook Integration

• Primary Hooks: resource_pre_fetch, resource_post_fetch
• Purpose: Prevent access to unauthorized file types
• Behavior: Block resource access if file type is not in allowlist

Configuration Schema

plugins:
  - name: "FileTypeAllowlist"
    kind: "plugins.file_type_allowlist.filter.FileTypeAllowlistPlugin"
    description: "Allow only configured file types for resources"
    version: "0.1.0"
    hooks: ["resource_pre_fetch", "resource_post_fetch"]
    mode: "enforce"
    priority: 20
    conditions:
      - resource_schemes: ["file", "http", "https"]
    config:
      # Allowed MIME types
      allowed_mime_types:
        - "text/plain"
        - "text/markdown"
        - "text/html"
        - "text/csv"
        - "application/json"
        - "application/xml"
        - "text/xml"
        - "application/yaml"
        - "text/yaml"
        - "application/pdf"
        - "image/png"
        - "image/jpeg"
        - "image/gif"
        - "image/webp"
      
      # Allowed file extensions  
      allowed_extensions:
        - ".md"
        - ".txt"
        - ".html"
        - ".htm"
        - ".json"
        - ".xml"
        - ".yaml"
        - ".yml"
        - ".csv"
        - ".pdf"
        - ".png"
        - ".jpg"
        - ".jpeg"
        - ".gif"
        - ".webp"
      
      # Blocked patterns (takes precedence over allowlist)
      blocked_patterns:
        - "*.exe"
        - "*.bat"
        - "*.cmd"
        - "*.ps1"
        - "*.sh"
        - "*.scr"
        - "*.com"
        - "*.pif"
      
      # MIME type detection settings
      mime_detection:
        enabled: true
        use_magic_numbers: true
        validate_extension_match: true
        trust_content_type_header: false
      
      # Error handling
      error_handling:
        block_message: "File type not allowed by security policy"
        include_allowed_types: true
        log_blocked_attempts: true
        
      # Special handling for different resource types
      resource_type_overrides:
        web_resources:
          schemes: ["http", "https"]
          additional_mime_types:
            - "application/javascript"
            - "text/css"
        local_files:
          schemes: ["file"]
          strict_extension_check: true
        
      # Content validation
      content_validation:
        max_file_size_mb: 100
        scan_content_headers: true
        validate_encoding: true
        
      # Allowlist exceptions
      exceptions:
        - resource_patterns: ["https://trusted-domain.com/*"]
          allow_all_types: true
        - user_roles: ["admin", "developer"]
          additional_extensions: [".py", ".js", ".sql"]

Implementation Requirements

File Structure

plugins/file_type_allowlist/
├── __init__.py
├── filter.py              # Main plugin class
├── mime_detector.py       # MIME type detection and validation
├── extension_checker.py   # File extension validation
├── content_validator.py   # Content-based validation
├── exceptions.py          # Exception handling logic
├── plugin-manifest.yaml   # Plugin metadata
└── README.md             # Usage documentation

Core Features

1. Multi-layered Validation

   • MIME type checking using magic numbers
   • File extension validation
   • Content-Type header verification
   • File size limitations

2. Comprehensive File Type Support

   • Text formats: TXT, MD, HTML, CSV
   • Data formats: JSON, XML, YAML
   • Document formats: PDF
   • Image formats: PNG, JPEG, GIF, WebP
   • Custom MIME type definitions

3. Security-First Approach

   • Blocklist for dangerous file types
   • Magic number validation to prevent spoofing
   • Extension/MIME type consistency checking
   • Content encoding validation

4. Flexible Configuration

   • Per-resource-type overrides
   • User role-based exceptions
   • Trusted domain allowlists
   • Custom error messages

Usage Examples

Basic File Type Filtering

# Resource request for allowed file type
resource_uri: "https://example.com/document.pdf"
# MIME type: application/pdf
# Extension: .pdf
# Result: Allowed (both in allowlist)

Blocked Executable File

# Resource request for dangerous file type
resource_uri: "https://malicious.com/virus.exe"
# MIME type: application/x-msdownload
# Extension: .exe
# Result: Blocked (executable file blocked)

MIME/Extension Mismatch Detection

# Resource with spoofed extension
resource_uri: "https://suspicious.com/document.txt"
# Actual MIME type: application/x-executable
# Declared extension: .txt
# Result: Blocked (MIME/extension mismatch)

Security Features

• Anti-Spoofing: Magic number validation prevents file type spoofing
• Comprehensive Blocklist: Blocks known dangerous file types
• Content Validation: Verifies file content matches declared type
• Size Limitations: Prevents resource exhaustion attacks

Testing Requirements

• Unit tests for MIME type detection accuracy
• File extension validation tests
• Magic number verification tests
• Spoofing attempt detection tests
• Performance tests with various file sizes
• Integration tests with different resource schemes

Documentation Requirements

• Plugin configuration guide with file type examples
• Security best practices for file type filtering
• MIME type reference documentation
• Troubleshooting guide for blocked files

Acceptance Criteria

• Plugin implements FileTypeAllowlistPlugin class
• Supports MIME type and file extension validation
• Magic number detection for anti-spoofing
• Configurable allowlist and blocklist management
• Resource type-specific overrides
• User role-based exceptions
• Comprehensive error handling and logging
• Plugin manifest and documentation created
• Unit tests with >90% coverage
• Security testing for spoofing attempts
• Performance benchmarks for large files

Priority

High - Important security feature

Dependencies

• python-magic for MIME type detection
• File type detection libraries
• Content validation utilities
• Pattern matching libraries

Security Considerations

• Prevent file type spoofing through magic number validation
• Secure handling of blocked file access attempts
• Audit logging for security monitoring
• Performance optimization to prevent DoS