threat-modeling.md

Threat Model Analysis for thoughtbot/paperclip

Threat: Unrestricted File Type Upload

• Threat: Unrestricted File Type Upload
• Description: An attacker uploads a malicious file (e.g., executable, HTML with XSS) by exploiting the lack of file type restrictions in Paperclip configuration. They might use a standard file upload form or API endpoint.
• Impact: Remote Code Execution (if executable), Cross-Site Scripting (XSS), or other attacks depending on the file type and application's handling.
• Paperclip Component Affected: content_type validation (lack of configuration or misconfiguration).
• Risk Severity: High
• Mitigation Strategies:
  • Whitelist allowed content types using validates_attachment_content_type with a strict list of MIME types.
  • Validate file extensions using validates_attachment_file_name with regular expressions to permit only allowed extensions.
  • Implement server-side validation exclusively, avoiding reliance on client-side checks.

Threat: Publicly Accessible Cloud Storage

• Threat: Publicly Accessible Cloud Storage
• Description: An attacker gains unauthorized access to uploaded files stored in cloud storage (e.g., AWS S3) due to misconfigured bucket permissions. They might use publicly available bucket URLs or enumeration techniques.
• Impact: Data breaches, exposure of sensitive information, unauthorized access to application assets.
• Paperclip Component Affected: Cloud storage integration (e.g., AWS S3 configuration).
• Risk Severity: Critical
• Mitigation Strategies:
  • Apply the Principle of Least Privilege when configuring cloud storage bucket permissions, restricting public access and granting only necessary permissions to the application.
  • Regularly audit cloud storage bucket permissions to ensure ongoing security.
  • Utilize IAM roles (for AWS) for application instances to access cloud storage, instead of embedding credentials directly in the application.
  • Employ private or pre-signed URLs for accessing files, enforcing authentication and authorization.

Threat: Insecure Local File System Storage

• Threat: Insecure Local File System Storage
• Description: An attacker gains unauthorized access to files stored on the local file system due to misconfigured web server or OS permissions. If stored within the web root, files might be directly accessible via URL.
• Impact: Data breaches, exposure of sensitive information, unauthorized access to application assets.
• Paperclip Component Affected: Local file system storage configuration.
• Risk Severity: High
• Mitigation Strategies:
  • Store files outside the web root by configuring Paperclip to use a directory outside the web server's document root.
  • Restrict file system permissions on the storage directory, limiting access to the application user and essential processes.
  • Implement application-level access control to authorize file access, even if storage is not directly accessible.

Threat: Image Processing Library Vulnerabilities

• Threat: Image Processing Library Vulnerabilities
• Description: An attacker uploads a specially crafted image file that exploits vulnerabilities in image processing libraries like ImageMagick used by Paperclip.
• Impact: Remote Code Execution, Denial of Service, or other impacts depending on the vulnerability exploited in the processing library.
• Paperclip Component Affected: Image processing functionality (reliant on external libraries like ImageMagick).
• Risk Severity: High
• Mitigation Strategies:
  • Maintain up-to-date processing libraries by regularly updating ImageMagick and other image processing libraries to their latest versions.
  • Restrict ImageMagick delegates to disable potentially dangerous features, if applicable and necessary for your use case.
  • Consider input sanitization of image files before processing as an advanced mitigation technique.