mitigations.md

Mitigation Strategies Analysis for miguelpruivo/flutter_file_picker

Mitigation Strategy: Strict File Type Validation

• Description:
  1. Developers: Identify the specific file types (e.g., images, documents, PDFs) that your application legitimately needs to process when using flutter_file_picker.
  2. Developers: Utilize the allowedExtensions parameter within the FilePicker.platform.pickFiles() function call. Provide a list of allowed file extensions (e.g., ['jpg', 'png', 'pdf']) that correspond to the necessary file types. Alternatively, use the type parameter with predefined types like FileType.image, FileType.video, FileType.audio, or FileType.custom for more control.
  3. Developers: Implement client-side checks immediately after the FilePicker.platform.pickFiles() function returns a result. Verify that the selected file's extension matches the allowed list. If an invalid file type is detected, display a clear error message to the user, informing them about the allowed file types and preventing further processing.
• List of Threats Mitigated:
  • Malicious File Upload (High Severity): Prevents users from selecting and potentially processing or uploading executable files (e.g., .exe, .sh, .bat) or files with embedded scripts (e.g., .html, .svg with JavaScript) disguised as allowed types, which could lead to client-side or server-side vulnerabilities if processed further.
  • Data Corruption/Application Errors (Medium Severity): Prevents the application from attempting to process files in unexpected formats that the application logic is not designed to handle, which could lead to crashes, errors, or data corruption within the Flutter application itself.
• Impact:
  • Malicious File Upload: Significantly reduces the risk by directly controlling the types of files that can be selected via flutter_file_picker, blocking a large category of potentially harmful files at the initial selection stage.
  • Data Corruption/Application Errors: Significantly reduces the risk of application instability and data integrity issues by ensuring that flutter_file_picker primarily facilitates the selection of file formats that the application is designed to handle.
• Currently Implemented: Yes, client-side validation using allowedExtensions is implemented in the file upload feature of the application, specifically within the file picking module that utilizes flutter_file_picker.
• Missing Implementation: No missing implementation directly related to flutter_file_picker for this strategy on the client-side.

Mitigation Strategy: Enforce File Size Limits

• Description:
  1. Developers: Determine reasonable maximum file size limits for each file type your application handles via flutter_file_picker, considering the application's client-side processing capabilities and user experience.
  2. Developers: On the client-side (within the Flutter app), immediately after a file is picked using FilePicker.platform.pickFiles(), access the size property of the returned PlatformFile object.
  3. Developers: Compare the retrieved file size against the defined maximum limit. If the file size exceeds the limit, display an informative error message to the user directly within the application, explaining the file size restriction and preventing further processing or actions with the selected file.
• List of Threats Mitigated:
  • Denial of Service (DoS) - Client-Side (Medium Severity): Prevents users from selecting extremely large files that could cause performance issues or crashes within the Flutter application itself due to excessive memory consumption or processing time on the client device.
  • Buffer Overflow/Memory Exhaustion - Client-Side (Low to Medium Severity): Reduces the risk of client-side vulnerabilities related to processing very large files in memory within the Flutter application, which could potentially lead to buffer overflows or memory exhaustion issues on the user's device.
• Impact:
  • Denial of Service (DoS) - Client-Side: Significantly reduces the risk of client-side performance degradation or crashes caused by users selecting excessively large files through flutter_file_picker.
  • Buffer Overflow/Memory Exhaustion - Client-Side: Partially mitigates the risk of client-side memory-related vulnerabilities by limiting the size of files handled by the Flutter application after selection via flutter_file_picker.
• Currently Implemented: Yes, a client-side file size limit of 10MB is implemented for file uploads within the application, enforced after file selection using flutter_file_picker.
• Missing Implementation: No missing implementation directly related to flutter_file_picker for this strategy on the client-side.

Mitigation Strategy: Sanitize and Validate File Paths (Internal Handling within Flutter App)

• Description:
  1. Developers: When handling file paths obtained from flutter_file_picker internally within your Flutter application's code, treat these paths as potentially untrusted input, even though flutter_file_picker is designed to return secure paths.
  2. Developers: Avoid directly using the raw path strings returned by flutter_file_picker in operations that could be vulnerable to path traversal or injection attacks within the Flutter application's file system interactions (though such vulnerabilities are less likely with flutter_file_picker itself).
  3. Developers: If you need to manipulate file paths within your Flutter code (e.g., constructing new paths based on user input and picked file paths), use secure path manipulation functions provided by Dart or platform-specific libraries. Ensure that any path manipulation is done safely and avoids introducing vulnerabilities.
  4. Developers: Avoid directly concatenating user-provided path segments with file paths obtained from flutter_file_picker. If path construction is necessary, use secure path joining methods.
• List of Threats Mitigated:
  • Path Traversal (Low Severity - unlikely with flutter_file_picker but good practice within Flutter app): While flutter_file_picker is designed to be secure, improper handling of file paths within the Flutter application's code could theoretically lead to path traversal if application logic is flawed in how it uses the returned paths. This mitigation is a preventative measure within the Flutter application itself.
  • File System Injection (Low Severity - unlikely with flutter_file_picker but good practice within Flutter app): Similar to path traversal, improper path handling within the Flutter application could in very specific scenarios lead to unintended file system operations if paths are constructed insecurely in the Flutter code.
• Impact:
  • Path Traversal: Minimally reduces the risk as flutter_file_picker itself is designed to return secure paths, but strengthens overall code security within the Flutter application by promoting secure path handling practices.
  • File System Injection: Minimally reduces the risk, acting as a defense-in-depth measure against potential vulnerabilities in path handling logic within the Flutter application.
• Currently Implemented: Yes, developers are generally following secure coding practices and avoiding direct path manipulation in file handling modules within the Flutter application.
• Missing Implementation: Formal code review process specifically focusing on secure file path handling within Flutter application's modules that use paths from flutter_file_picker could be implemented.

Mitigation Strategy: Minimize Required Permissions for File Access

• Description:
  1. Developers: Carefully review your Flutter application's permission requests, specifically those related to storage access that are necessary for flutter_file_picker to function.
  2. Developers: Only request the minimum necessary permissions required for the intended file picking functionality. Avoid requesting broad storage access permissions (e.g., READ_EXTERNAL_STORAGE on Android) if your application only needs to access files explicitly selected by the user through flutter_file_picker.
  3. Developers: Explore and utilize platform-specific APIs or scoped storage mechanisms where possible to further limit the application's access to the file system. Aim to restrict access to only the files selected by the user via flutter_file_picker, rather than granting broad storage permissions that are not essential.
• List of Threats Mitigated:
  • Data Breach/Unauthorized Access (Medium Severity): If the Flutter application itself is compromised, limiting storage permissions restricts the potential attacker's ability to access sensitive data stored on the user's device. Broad storage permissions granted for flutter_file_picker usage, if unnecessary, increase the potential scope of a data breach originating from the compromised application.
  • Privacy Violation (Medium Severity): Requesting unnecessary broad storage permissions for file picking functionality using flutter_file_picker can be perceived as a privacy violation by users, as it suggests the application might access more data than it legitimately needs for its file picking features.
• Impact:
  • Data Breach/Unauthorized Access: Partially mitigates the risk by limiting the attack surface and potential data exposure in case of a compromise of the Flutter application, specifically concerning file system access related to flutter_file_picker.
  • Privacy Violation: Improves user privacy and trust by demonstrating that the Flutter application adheres to the principle of least privilege and only requests storage permissions that are demonstrably necessary for its file picking functionality using flutter_file_picker.
• Currently Implemented: Yes, the Flutter application currently requests only necessary storage permissions that are deemed essential for the file picking functionality provided by flutter_file_picker.
• Missing Implementation: Implement a process for regular review of permission requests during development cycles to ensure they remain minimal and justified, specifically in the context of how flutter_file_picker is used and the permissions it necessitates.

Mitigation Strategy: Regularly Update flutter_file_picker Package

• Description:
  1. Developers: Establish a routine to regularly check for updates to the flutter_file_picker package on pub.dev, the official package repository for Flutter.
  2. Developers: Utilize the flutter pub outdated command in your Flutter project to proactively identify outdated dependencies, including flutter_file_picker.
  3. Developers: When updates are available, update the flutter_file_picker package to the latest stable version using the command flutter pub upgrade flutter_file_picker.
  4. Developers: After updating, carefully review the changelog or release notes of the updated flutter_file_picker package to understand any bug fixes, new features, or, importantly, security improvements that are included in the update.
• List of Threats Mitigated:
  • Exploitation of Known Vulnerabilities (High Severity): Outdated versions of flutter_file_picker may contain known security vulnerabilities that have been identified and patched in newer versions. Failing to regularly update the package leaves the Flutter application vulnerable to potential exploits targeting these known security issues within the flutter_file_picker package itself.
• Impact:
  • Exploitation of Known Vulnerabilities: Significantly reduces the risk of exploitation by ensuring that the Flutter application benefits from the latest security patches, bug fixes, and improvements incorporated into the flutter_file_picker package by its maintainers.
• Currently Implemented: No, package updates, including flutter_file_picker, are not performed regularly as a standard part of the development cycle. Updates are typically done reactively rather than proactively.
• Missing Implementation: Implement a proactive and scheduled process for regularly checking and updating all Flutter project dependencies, with a specific focus on flutter_file_picker, as part of routine maintenance and security best practices.

Mitigation Strategy: Implement Content Security Policy (CSP) if Handling Web Files Picked by flutter_file_picker

• Description:
  1. Developers (Specifically for web deployments of the Flutter application): If your Flutter application is deployed to the web platform and utilizes files picked via flutter_file_picker in a web context (e.g., displaying images, documents, or other file content within a web view or iframe), it is crucial to configure and implement a Content Security Policy (CSP) for your web application.
  2. Developers: Define a robust CSP that restricts the sources from which various resources (such as scripts, stylesheets, images, fonts, and other assets) can be loaded by the web application. Also, restrict the actions that web pages are permitted to perform (e.g., inline script execution, form submissions to external origins).
  3. Developers: Implement the defined CSP by configuring your web server to send the Content-Security-Policy HTTP header with the appropriate directives in the server's responses. This header instructs the user's browser to enforce the security policy for your web application.
• List of Threats Mitigated:
  • Cross-Site Scripting (XSS) (High Severity - in web context): If a malicious file (e.g., a manipulated image or document containing embedded scripts) is processed and subsequently displayed in a web view or iframe within the web-deployed Flutter application, a properly configured CSP can effectively prevent the execution of these embedded scripts or the loading of malicious external resources. This significantly mitigates the risk of XSS attacks that could arise from handling files picked by flutter_file_picker in a web environment.
  • Content Injection Attacks (Medium Severity - in web context): CSP can also help prevent various other types of content injection attacks in the web context by strictly controlling the origins and types of content that the web application is allowed to load and process, even when dealing with files selected via flutter_file_picker.
• Impact:
  • Cross-Site Scripting (XSS): Significantly reduces the risk of XSS attacks in web deployments of the Flutter application, particularly when handling and displaying files picked using flutter_file_picker, by enforcing strict controls over script execution and resource loading.
  • Content Injection Attacks: Partially mitigates the risk of various content injection attacks in the web context by enforcing restrictions on content sources and types, enhancing the security of the web application when processing files from flutter_file_picker.
• Currently Implemented: No, Content Security Policy (CSP) is not currently implemented for the web deployment of the Flutter application. The application lacks CSP headers in its web server configuration.
• Missing Implementation: Implement CSP for the web application deployment. This is particularly critical for pages or components that handle, display, or process files that have been picked using flutter_file_picker, to ensure robust client-side security in the web environment.