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Threat Model Analysis for miguelpruivo/flutter_file_picker

Threat: File Type Spoofing / Masquerading (via extension property)

  • Threat: File Type Spoofing / Masquerading (via extension property)

    • Description: An attacker crafts a malicious file with a misleading file extension (e.g., a .exe disguised as a .pdf). The user, deceived by the extension displayed in the file picker dialog, selects the file. The flutter_file_picker package returns this misleading extension to the application. The application, if it relies solely on this extension, is then vulnerable.
    • Impact:
      • Code Execution: If the application attempts to execute the disguised file based on the incorrect extension provided by flutter_file_picker, it could lead to arbitrary code execution.
      • Data Corruption/Exfiltration: Processing the file as the wrong type (again, based on the incorrect extension from the picker) can lead to corruption or data theft.
    • Affected Component:
      • FilePickerResult.files: Specifically, the extension property of the PlatformFile objects within the files list. This property is directly populated by flutter_file_picker based on the file name and is the source of the misleading information.
    • Risk Severity: Critical
    • Mitigation Strategies:
      • Content-Based Type Detection: Never rely solely on the extension property provided by flutter_file_picker. Implement robust content-based type detection using libraries that analyze the file's actual contents (magic numbers, headers, etc.).
      • MIME Type Validation (Web, as a supplement): On the web, use the type property of PlatformFile (MIME type) in addition to, but not as a replacement for, content-based validation. The MIME type can also be spoofed, but it provides an extra check.
      • Sandboxing: Process the file in a sandboxed environment to limit the impact of potential code execution.

Threat: Denial of Service (DoS) via Large Files (unchecked size property)

  • Threat: Denial of Service (DoS) via Large Files (unchecked size property)

    • Description: An attacker selects an extremely large file through the file picker. The flutter_file_picker package correctly reports the file's size via the size property. However, if the application fails to check this size property before attempting to read the file, it can lead to a denial-of-service attack.
    • Impact:
      • Application Crash: The application runs out of memory and crashes due to attempting to load the entire large file.
      • Device Unresponsiveness: The device becomes unresponsive due to excessive memory consumption.
    • Affected Component:
      • FilePickerResult.files: Specifically, the size property of the PlatformFile objects. The vulnerability is the application's failure to use this information provided by flutter_file_picker.
    • Risk Severity: High
    • Mitigation Strategies:
      • Mandatory File Size Limit: Always check the size property of the PlatformFile object before attempting any file operations. Enforce a strict maximum file size limit.
      • Streaming (for large file support): If handling potentially large files is necessary, use the readStream property (and handle it correctly) to process the file in chunks, avoiding loading the entire file into memory at once.

Threat: Denial of Service (DoS) via Malicious File Content (unchecked file handling after selection)

  • Threat: Denial of Service (DoS) via Malicious File Content (unchecked file handling after selection)

    • Description: An attacker selects a specially crafted file (e.g., a "zip bomb" or a file designed to cause excessive processing) through the file picker. While flutter_file_picker itself doesn't process the file content, it provides the means (path or stream) to access the file. If the application doesn't properly validate or limit the processing of this file after selection, it can lead to a DoS.
    • Impact:
      • Application Crash: Resource exhaustion (CPU, memory, disk) causes the application to crash.
      • Device Unresponsiveness: The device becomes slow or unresponsive.
      • Disk Space Exhaustion: (Specifically for attacks like zip bombs)
    • Affected Component:
      • FilePickerResult.files: The path and readStream properties are the means by which the application accesses the potentially malicious file. The vulnerability is in the subsequent handling of the file by the application, but the picker provides the entry point.
    • Risk Severity: High
    • Mitigation Strategies:
      • Strict Resource Limits: Enforce strict limits on memory, CPU time, and disk space during file processing.
      • Specialized Input Validation: Implement checks for known malicious file types or structures (e.g., zip bomb detection).
      • Sandboxing: Process the file in a sandboxed environment to contain the damage.
      • Decompression Limits (for archives): If the application decompresses archives, set limits on expansion ratio, file count, and uncompressed size.