attack-surface.md

Attack Surface Analysis for miguelpruivo/flutter_file_picker

Attack Surface: Path Traversal / Directory Traversal

• Description: An attacker manipulates file paths to access files or directories outside the intended application sandbox or allowed directories.
  • flutter_file_picker Contribution: The package is the direct source of the file path (or File object) provided to the application. While the underlying OS file picker should have some protections, flutter_file_picker acts as the intermediary, and any flaws in its handling of paths or reliance on unvalidated OS behavior could be exploited. This is especially relevant if the package doesn't properly canonicalize paths before returning them to the application.
  • Example: A vulnerability exists within flutter_file_picker (or a platform-specific implementation it uses) that fails to properly handle symbolic links or specially crafted filenames before passing the path to the application. The attacker exploits this vulnerability to make the package return a malicious path, even if the user appears to select a safe file.
  • Impact:
    • Read access to arbitrary files (sensitive data, configuration files, etc.).
    • Write access to arbitrary files (overwriting system files, injecting malicious code, data corruption).
    • Potential for code execution.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Developer (of flutter_file_picker):
      • Robust Path Handling: Ensure the package itself performs thorough path validation and canonicalization before returning any path to the calling application. This includes handling symlinks, relative paths, and platform-specific path separators correctly. Use well-tested, platform-specific APIs for path manipulation.
      • Security Audits: Regularly audit the package's code, particularly the platform-specific implementations, for path traversal vulnerabilities.
      • Fuzz Testing: Use fuzz testing to test the package with a wide range of unexpected and potentially malicious file paths and names.
    • Developer (of the using application):
      • Assume Untrusted Input: Treat the path returned by flutter_file_picker as completely untrusted, even if the package is believed to be secure. Implement all the mitigation strategies described in the previous, more comprehensive list (whitelisting, canonicalization, etc.). Never rely solely on the package for security.
    • User:
      • Keep flutter_file_picker updated to the latest version to benefit from any security patches.

Attack Surface: File Type Confusion / MIME Type Spoofing (related to filtering)

• Description: An attacker exploits vulnerabilities in how flutter_file_picker implements its file type filtering (by extension or MIME type) to bypass these filters.
  • flutter_file_picker Contribution: The package provides functionality to filter files based on extension and MIME type. If this filtering is implemented incorrectly within the package, an attacker could bypass it. This is distinct from the application misusing the results of the filtering.
  • Example: A bug in flutter_file_picker's extension filtering logic allows an attacker to select a file with a .exe extension even when the filter is set to only allow .txt files. This is a package vulnerability, not an application misuse. Or, the package incorrectly parses MIME types provided by the underlying OS, allowing a spoofed MIME type to bypass the filter.
  • Impact:
    • Allows the selection of files that should have been blocked by the filter, potentially leading to the application processing unexpected file types. This increases the risk of subsequent vulnerabilities in the application if it doesn't perform its own content-based type validation.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developer (of flutter_file_picker):
      • Robust Filter Implementation: Ensure the file type filtering logic is robust and correctly handles edge cases, including variations in extension casing, MIME type formatting, and platform-specific differences.
      • Regular Expression Validation: Use well-tested regular expressions (or equivalent platform-specific mechanisms) to validate extensions and MIME types.
      • Unit Tests: Thoroughly test the filtering functionality with a wide range of valid and invalid file types and names.
    • Developer (of the using application):
      • Content-Based Type Detection: Always perform content-based type detection after receiving the file from flutter_file_picker. Do not rely solely on the package's filtering.
    • User:
      • Keep flutter_file_picker updated.