mitigations.md

Mitigation Strategies Analysis for thephpleague/flysystem

Mitigation Strategy: Implement Least Privilege Principle for Adapter Configuration

• Description:
  1. When setting up Flysystem adapters (like local, AWS S3, FTP), carefully review the permissions granted to the credentials used by the adapter.
  2. For each adapter, configure the credentials to have the absolute minimum permissions necessary for the application to function correctly with Flysystem. Avoid granting broad or administrative privileges.
  3. For example, if using the AWS S3 adapter for user uploads, configure the IAM role or access keys to only allow s3:GetObject, s3:PutObject, and s3:DeleteObject actions on the specific S3 bucket and path prefix used by Flysystem, and nothing more.
  4. Regularly audit and review these adapter configurations to ensure permissions remain minimal and aligned with the application's needs.
• Threats Mitigated:
  • Unauthorized Access (High Severity) - Limits the potential damage if Flysystem adapter credentials are compromised. An attacker would only gain access within the scope of the limited permissions granted to the adapter.
  • Data Breach (High Severity) - Reduces the risk of a large-scale data breach. Even with compromised adapter credentials, the attacker's ability to access or modify data is restricted to the minimal permissions configured for Flysystem.
• Impact:
  • Unauthorized Access: High Reduction
  • Data Breach: High Reduction
• Currently Implemented:
  • Yes, for the AWS S3 adapter used for user uploads. An IAM role is configured with restricted permissions to a specific S3 bucket and path prefix (/user-uploads/*), allowing only necessary actions like GetObject, PutObject, and DeleteObject. This is defined in config/filesystems.php and managed within AWS IAM.
• Missing Implementation:
  • For the local filesystem adapter used for temporary file processing, the principle is partially applied through web server user permissions. However, it could be further improved by using a dedicated system user with even more restricted permissions specifically for the temporary directory used by Flysystem (/tmp/app-temp/).

Mitigation Strategy: Utilize Flysystem's Path Prefixing and Scoping

• Description:
  1. When configuring Flysystem adapters, use the pathPrefix option. This option effectively restricts all file operations performed through that specific Flysystem instance to a defined subdirectory or path within the storage backend.
  2. Structure your application's file storage logically and use pathPrefix to create isolated Flysystem instances for different parts of your application or user groups. This ensures operations in one area cannot inadvertently affect others.
  3. Ensure all application code interacting with Flysystem respects the configured pathPrefix. Avoid bypassing Flysystem and directly accessing storage paths outside of the defined prefix, as this would negate the security benefit.
• Threats Mitigated:
  • Path Traversal (Medium Severity) - Even if path traversal vulnerabilities exist in application code, pathPrefix acts as a security boundary, preventing access to files outside the designated prefixed path within the storage system.
  • Accidental Data Modification/Deletion (Medium Severity) - Reduces the risk of accidental operations affecting unintended areas of storage due to programming errors or misconfigurations, as Flysystem operations are scoped to the defined prefix.
• Impact:
  • Path Traversal: Medium Reduction
  • Accidental Data Modification/Deletion: Medium Reduction
• Currently Implemented:
  • Yes, for the AWS S3 user uploads adapter. The pathPrefix is set to /user-uploads/ in config/filesystems.php. This ensures all user file operations through this Flysystem instance are contained within the /user-uploads/ directory of the S3 bucket.
• Missing Implementation:
  • The local filesystem adapter for temporary files does not currently utilize pathPrefix. It should be configured with a pathPrefix pointing to the dedicated temporary directory to further isolate temporary file operations and prevent accidental access to other parts of the local filesystem via Flysystem.

Mitigation Strategy: Utilize Flysystem's Path Manipulation Functions Safely

• Description:
  1. When manipulating file paths within your application code that will be used with Flysystem, prefer to use Flysystem's built-in path manipulation functions (if provided by the specific adapter and relevant context).
  2. If Flysystem doesn't provide specific path manipulation functions for your adapter or use case, rely on secure path manipulation libraries or built-in language functions that are designed to prevent path traversal and other path-related vulnerabilities.
  3. Avoid constructing or manipulating paths using string concatenation or regular expressions directly on user-provided input without careful validation and sanitization.
  4. Be cautious when using functions that might resolve relative paths or normalize paths in unexpected ways, as these could potentially be exploited to bypass path restrictions.
• Threats Mitigated:
  • Path Traversal (Medium Severity) - Reduces the risk of introducing path traversal vulnerabilities through insecure path manipulation in application code when interacting with Flysystem.
  • Injection Attacks (Indirect, Low Severity) - Minimizes the potential for indirect injection attacks that might be triggered by manipulating file paths in unexpected ways, although Flysystem itself provides a layer of abstraction.
• Impact:
  • Path Traversal: Medium Reduction
  • Injection Attacks (Indirect): Low Reduction
• Currently Implemented:
  • Partially implemented. The application uses some built-in PHP path functions like basename() and dirname() in file handling logic. However, there isn't a systematic approach to exclusively using Flysystem's path manipulation features (as adapter support varies).
• Missing Implementation:
  • Explore and document the path manipulation functions offered by the specific Flysystem adapters in use. Develop coding guidelines to encourage developers to prioritize using these functions or secure path manipulation libraries over manual string manipulation when working with file paths in Flysystem contexts.