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attack-surface.md

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Attack Surface Analysis for miguelpruivo/flutter_file_picker

Attack Surface: Unvalidated File Upload/Selection

  • Description: The application accepts files selected by the user via flutter_file_picker without proper validation of file type, content, or size. This lack of validation is a direct consequence of how developers might use flutter_file_picker without implementing sufficient security measures after file selection.
  • How flutter_file_picker contributes: flutter_file_picker's core function is to enable file selection. It provides the mechanism for users to choose files, and returns file paths to the application. It does not inherently validate the content or safety of these files. This responsibility falls entirely on the application developer using the package. By providing this file selection capability without built-in validation, flutter_file_picker directly enables this attack surface if not handled securely by the application.
  • Example: A user, intending to exploit a vulnerability, selects a file named "document.pdf.exe". The application, using flutter_file_picker to get the file path, proceeds to process this file assuming it's a PDF based on the initial filter or lack thereof, without validating its actual content. This could lead to execution of the malicious executable.
  • Impact:
    • Malware infection of user devices or server systems.
    • Data breaches if malicious files exploit vulnerabilities to access sensitive information or if uploaded files themselves contain sensitive data that is then improperly processed or stored.
    • Denial of Service (DoS) if large or specially crafted files are uploaded and overwhelm application resources or cause crashes.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developer:
      • Mandatory Server-Side Validation: Always perform robust server-side validation of file type, size, and content after the file is uploaded. Rely on techniques like magic number analysis, not just file extensions, to determine file type.
      • Client-Side Pre-Validation (Enhancement, Not Security): Implement client-side checks for file type and size as a user experience improvement and to reduce unnecessary server load, but never rely on client-side validation for security.
      • Strict File Type Whitelisting: Define and enforce a strict whitelist of allowed file types. Only permit file types that are absolutely necessary for the application's functionality.
      • Enforce File Size Limits: Implement and enforce reasonable file size limits to prevent DoS attacks and resource exhaustion.
      • Implement Virus Scanning and Malware Detection: Integrate server-side virus scanning and malware detection tools to scan uploaded files, especially if they are processed or stored by the application.
      • Utilize Sandboxing and Isolation: Process uploaded files in isolated environments (sandboxes, containers) to limit the potential damage if malicious code is executed.
    • User:
      • Be Cautious with File Selection: Be mindful of the files you select and upload, especially to untrusted applications. Verify the file source and type before uploading. (User mitigation is limited as the primary responsibility lies with the application developer).