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mitigations.md

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Mitigation Strategies Analysis for miguelpruivo/flutter_file_picker

Mitigation Strategy: Strict File Type Validation (Using allowedExtensions - Client-Side)

  • Description:

    1. Client-Side (Flutter): Utilize the allowedExtensions parameter within the FilePicker.platform.pickFiles() method. This provides an initial, user-experience-focused filter, guiding the user towards selecting appropriate file types. It is not a robust security control on its own.
    2. Example: 
      FilePickerResult? result = await FilePicker.platform.pickFiles(
  allowedExtensions: ['jpg', 'jpeg', 'png', 'pdf'],
  type: FileType.custom, // Required when using allowedExtensions
);
    3. Clearly communicate to the user which file types are permitted.

  • Threats Mitigated:

    • Malicious File Uploads (Low Severity - Client-Side Only): Minimally reduces the likelihood of a user selecting an obviously incorrect file type. It does not prevent a determined attacker.
    • File Type Spoofing (Low Severity - Client-Side Only): Easily bypassed; provides no real protection against spoofing.

  • Impact:

    • Malicious File Uploads: Very low impact on security. Primarily a usability feature.
    • File Type Spoofing: Negligible impact.

  • Currently Implemented:

    • Used in lib/widgets/file_upload_widget.dart.

  • Missing Implementation:

    • None, from the perspective of using flutter_file_picker. The crucial missing piece is the robust server-side validation, which is outside the scope of this narrowed-down list.

Mitigation Strategy: Principle of Least Privilege (Using withReadAccess and withWriteAccess)

  • Description:

    1. Client-Side (Flutter): When calling FilePicker.platform.pickFiles(), use the withReadAccess and withWriteAccess boolean parameters judiciously.
    2. Set withReadAccess: true only if you need to read the contents of the selected file. This is almost always the case.
    3. Set withWriteAccess: true only if you absolutely need to modify the selected file. This is rarely needed when using a file picker for uploads. Avoid it if possible.
    4. Example (Read-Only - Typical): 
      FilePickerResult? result = await FilePicker.platform.pickFiles(
  withReadAccess: true,
  withWriteAccess: false, // Usually the correct setting for uploads
);
    5. Example (Read-Write - Rarely Needed): 
      FilePickerResult? result = await FilePicker.platform.pickFiles(
  withReadAccess: true,
  withWriteAccess: true, // Only if you need to modify the selected file
);

  • Threats Mitigated:

    • Improper Permissions (Medium Severity): Reduces the potential impact of vulnerabilities by limiting the application's access to the file system. If an attacker could exploit a vulnerability, the damage would be limited by the restricted permissions.

  • Impact:

    • Improper Permissions: Minimizes the potential damage from a successful exploit.

  • Currently Implemented:

    • withReadAccess: true and withWriteAccess: false are correctly used in lib/widgets/file_upload_widget.dart.

  • Missing Implementation:

    • None, from the perspective of correctly using flutter_file_picker. The broader context of requesting appropriate permissions in the Android Manifest and iOS Info.plist is outside the scope of this list.

Mitigation Strategy: Review flutter_file_picker's Behavior (UI/UX)

  • Description:

    1. Development/Testing:
      • Thoroughly test the flutter_file_picker's UI and behavior on all supported platforms (Android, iOS, web). This is about observing how the picker itself behaves.
      • Pay close attention to how the file picker displays file paths, directory structures, and file metadata.
      • Ensure that the picker does not inadvertently reveal any sensitive information about the file system, server details, or other potentially exploitable data. The picker should only show information relevant to the user's selection.
      • Test with different file system configurations (e.g., different storage locations, symbolic links) and user permissions to identify any platform-specific differences or potential information leaks.

  • Threats Mitigated:

    • Information Disclosure (Low Severity): Reduces the risk of the file picker itself leaking sensitive information through its user interface.

  • Impact:

    • Information Disclosure: Minimizes the risk of unintentional information disclosure via the file picker's UI.

  • Currently Implemented:

    • Basic UI testing has been performed on Android and iOS.

  • Missing Implementation:

    • More comprehensive testing is needed, especially on the web platform and with various file system configurations and user permission levels. This should be part of the regular testing process.