threat-modeling.md

Threat Model Analysis for miguelpruivo/flutter_file_picker

Threat: Malicious File Selection - Malware Injection

Description: An attacker could socially engineer a user to select a malicious file (e.g., malware disguised as a PDF or image) using the file picker. The flutter_file_picker itself facilitates the file selection process. If the application then processes this file without robust content validation, the malware could be executed within the application's context or on the user's device, leading to severe compromise. The attacker exploits the application's trust in user-selected files and lack of content security checks after file picking.

Impact: Critical. Complete compromise of the user's device or application environment. Malware execution can lead to data theft, data corruption, unauthorized access to sensitive information, remote control of the device, and denial of service. This can severely damage the user's privacy, security, and the application's reputation.

Affected Component: Application's file processing logic initiated after file selection via flutterFilePicker(). While flutter_file_picker is the entry point, the vulnerability lies in the subsequent processing.

Risk Severity: High to Critical (depending on the potential impact of malware execution in the application's context and on the device).

Mitigation Strategies:

• Mandatory Content Validation: Developers must implement rigorous server-side or client-side validation of the file content after it is picked. File extension validation is insufficient.
• Deep File Inspection: Employ techniques like magic number verification and content-based analysis to accurately determine file type and detect potentially malicious files.
• Sandboxed Processing: If possible, process user-uploaded files in a sandboxed environment to limit the potential damage from malware execution.
• Antivirus/Malware Scanning: Integrate with antivirus or malware scanning services, especially for server-side file processing, to proactively detect and block malicious files.
• Principle of Least Privilege: Minimize the permissions granted to the application and the user account under which the application processes files to limit the impact of potential malware execution.
• User Education: Educate users about the risks of selecting files from untrusted sources and the importance of only selecting files they expect to be processed by the application.

Threat: Unintended Broad File System Access Leading to Critical Data Exposure

Description: Developers might misconfigure flutter_file_picker by using overly permissive settings (e.g., FileType.any without sufficient allowedExtensions restrictions) or by requesting access to broad directory structures. This can unintentionally grant the application access to a much wider range of the user's file system than necessary. An attacker, or even a curious user, could exploit this by navigating through the file picker to sensitive directories and potentially accessing critical user data that the application was not intended to access. While flutter_file_picker itself doesn't directly exfiltrate data, it provides the access mechanism that can be misused if the application has further vulnerabilities or if the user is tricked into granting excessive permissions.

Impact: High to Critical. Data Confidentiality breach of highly sensitive user data. Exposure of critical personal information, financial records, private documents, or system files. This can lead to identity theft, financial loss, reputational damage, and severe privacy violations. The severity escalates to critical if the exposed data is highly sensitive and the potential for harm is significant.

Affected Component: flutter_file_picker configuration parameters (type, allowedExtensions, initialDirectory) and the application's permission request logic.

Risk Severity: High (can escalate to Critical depending on the sensitivity of data potentially exposed).

Mitigation Strategies:

• Strictly Limit File Scope: Developers must meticulously define the FileType and allowedExtensions to the absolute minimum required for the application's intended functionality. Avoid FileType.any unless absolutely necessary and heavily restricted by allowedExtensions.
• Principle of Least Privilege (Permissions): Request the narrowest possible file system access permissions from the user. Justify each permission request clearly to the user.
• Directory Guidance (with caution): Use initialDirectory to guide users to the expected file locations, but remember users can still navigate outside this directory. This is a usability aid, not a security control.
• Regular Security Audits: Conduct regular security audits of the application's file access configurations and code to ensure that file access is appropriately restricted and that no unintended broad access is granted.
• User Awareness and Transparency: Clearly communicate to users the specific purpose and scope of file access permissions requested by the application. Be transparent about the types of files the application needs to access and why.
• Minimize Data Exposure: Design the application to minimize the need to access the user's file system in the first place. Explore alternative approaches if possible.