Skip to content

Latest commit

 

History

History
220 lines (180 loc) · 20.5 KB

sec-design-deep-analysis.md

File metadata and controls

220 lines (180 loc) · 20.5 KB

Deep Analysis of FlorisBoard Security

1. Objective, Scope, and Methodology

Objective: To conduct a thorough security analysis of the FlorisBoard Android keyboard application, focusing on identifying potential vulnerabilities and recommending mitigation strategies. The analysis will cover key components, data flows, and architectural aspects, with a particular emphasis on the unique security challenges inherent in an input method application.

Scope:

  • Codebase: The FlorisBoard codebase hosted at https://github.com/florisboard/florisboard.
  • Documentation: Available documentation on GitHub, including README, wiki, and any other relevant project documentation.
  • Inferred Architecture: The application's architecture and data flow as inferred from the codebase and documentation.
  • Key Components:
    • Input Method Service (IME) interaction with the Android system.
    • UI Component (handling user interaction and display).
    • Logic Component (input processing, prediction, correction).
    • Data Storage (user dictionaries, settings).
    • Theme and Extension Handling (if applicable).
    • Build and Deployment Processes.

Methodology:

  1. Architecture and Data Flow Analysis: Infer the application's architecture and data flow based on the provided C4 diagrams, codebase, and documentation. Identify critical data paths and potential attack surfaces.
  2. Component-Specific Security Review: Analyze each key component identified in the scope for potential vulnerabilities, considering the specific context of an input method application.
  3. Threat Modeling: Identify potential threats based on the business risks, accepted risks, and identified vulnerabilities. Prioritize threats based on likelihood and impact.
  4. Mitigation Strategy Recommendation: Propose specific, actionable mitigation strategies for each identified threat, tailored to the FlorisBoard project.
  5. Review of Existing Security Controls: Evaluate the effectiveness of existing security controls and identify any gaps.
  6. Address Questions and Assumptions: Provide insights and recommendations related to the open questions and assumptions.

2. Security Implications of Key Components

This section breaks down the security implications of each key component, drawing inferences from the codebase structure and available documentation.

2.1 Input Method Service (IME) Interaction:

  • Security Implications: The IME is the core of the keyboard and the primary interface with the Android system. It's a privileged component that can access all text input. A compromised IME can capture everything a user types, including passwords, credit card numbers, and private communications. The Android system provides sandboxing and permission controls, but vulnerabilities in the IME's interaction with the system could bypass these protections.
  • Specific Threats:
    • Privilege Escalation: A vulnerability in the IME could allow it to gain higher privileges than intended, potentially accessing other applications' data or system resources.
    • Inter-Process Communication (IPC) Vulnerabilities: The IME communicates with other applications via the Android system. Vulnerabilities in this communication (e.g., intent spoofing, injection attacks) could allow malicious applications to intercept or manipulate input data.
    • Denial of Service: A crashing or unresponsive IME can prevent the user from using their device.
  • Mitigation Strategies:
    • Strict Adherence to Android's IME API: Avoid using undocumented or deprecated APIs.
    • Thorough Input Validation: Sanitize all data received from the Android system (e.g., text input events, configuration changes).
    • Secure IPC: Use secure IPC mechanisms provided by Android (e.g., bound services with explicit intents and permissions). Validate all data received from other applications.
    • Robust Error Handling: Implement robust error handling to prevent crashes and ensure the IME remains responsive.
    • Fuzz Testing: Perform fuzz testing on the IME's interface with the Android system to identify potential vulnerabilities.

2.2 UI Component (Kotlin/Jetpack Compose):

  • Security Implications: The UI component handles user interaction and displays the keyboard. While primarily focused on presentation, it's the entry point for user input and therefore a potential target for attacks.
  • Specific Threats:
    • Input Validation Issues: Failure to properly sanitize user input (e.g., touch events, gestures) could lead to unexpected behavior or vulnerabilities.
    • Overlay Attacks: A malicious application could attempt to overlay the keyboard UI with a fake UI to capture user input (though this is primarily mitigated by the Android system).
    • UI Redressing: Subtle modifications to the UI could trick users into entering sensitive information in the wrong context.
  • Mitigation Strategies:
    • Input Validation: Validate all user input, including touch events and gestures. Ensure that input is handled consistently and securely.
    • Secure UI Rendering: Use secure UI rendering techniques to prevent overlay attacks and UI redressing. Leverage Android's built-in security features for UI protection.
    • Accessibility Considerations: Ensure that accessibility features (e.g., TalkBack) are implemented securely and do not introduce vulnerabilities.

2.3 Logic Component (Kotlin):

  • Security Implications: This component contains the core logic for text prediction, correction, and other keyboard features. It's a critical area for security as it processes user input and interacts with data storage.
  • Specific Threats:
    • Logic Errors: Bugs in the prediction or correction algorithms could lead to unintended behavior or vulnerabilities.
    • Side-Channel Attacks: The timing or resource usage of the logic component could potentially leak information about user input.
    • Data Leakage: Improper handling of user input data within the logic component could lead to data leakage.
  • Mitigation Strategies:
    • Secure Coding Practices: Follow secure coding practices to minimize logic errors and vulnerabilities.
    • Input Validation: Sanitize all data used within the logic component, including data from data storage and the UI component.
    • Memory Management: Carefully manage memory to prevent buffer overflows and other memory-related vulnerabilities.
    • Constant-Time Operations: Consider using constant-time algorithms for sensitive operations (e.g., password handling) to mitigate side-channel attacks.
    • Code Review: Thoroughly review the code in the logic component for potential security issues.

2.4 Data Storage (Local Files/Database):

  • Security Implications: This component stores user dictionaries, settings, and potentially other data. Protecting this data is crucial for user privacy.
  • Specific Threats:
    • Unauthorized Access: Other applications or malicious actors could attempt to access the keyboard's data storage.
    • Data Corruption: Errors in data storage could lead to data loss or corruption.
    • Data Leakage: Data could be leaked through backups, logs, or other mechanisms.
  • Mitigation Strategies:
    • Encryption at Rest: Encrypt the user dictionary and other sensitive data stored on the device. Use strong encryption algorithms (e.g., AES-256) and securely manage the encryption keys. Consider using Android's Keystore system for key management.
    • Least Privilege: Access data storage only when necessary and with the minimum required permissions.
    • Secure File Permissions: Use appropriate file permissions to restrict access to the keyboard's data.
    • Data Validation: Validate data read from storage to prevent injection attacks or corruption issues.
    • Backup Considerations: If backups are supported, ensure that they are handled securely and that user data is encrypted during backup and restore. Consider allowing users to opt out of backups.

2.5 Theme and Extension Handling:

  • Security Implications: Custom themes and extensions can significantly enhance the keyboard's functionality and appearance, but they also introduce a significant security risk. If not properly vetted, they could contain malicious code.
  • Specific Threats:
    • Malicious Code Injection: Themes or extensions could inject malicious code into the keyboard, allowing attackers to capture user input, access data, or perform other malicious actions.
    • Privilege Escalation: A malicious extension could attempt to gain higher privileges than intended.
    • Data Leakage: Extensions could leak user data to third parties.
  • Mitigation Strategies:
    • Sandboxing: Run themes and extensions in a sandboxed environment with limited permissions. This is the most critical mitigation. Consider using a separate process or a restricted context for extensions.
    • Code Signing: Require themes and extensions to be digitally signed by trusted developers.
    • Manifest Permissions: Define a clear set of permissions that extensions can request. Limit these permissions to the minimum necessary.
    • User Review and Approval: Implement a system for users to review and approve the permissions requested by extensions.
    • Static and Dynamic Analysis: Perform static and dynamic analysis of themes and extensions before allowing them to be installed.
    • Content Security Policy (CSP): If extensions involve any web-based content, implement a strict CSP to prevent cross-site scripting (XSS) and other web-based attacks.
    • Regular Audits: Regularly audit the code of popular themes and extensions.
    • Vulnerability Disclosure Program: Encourage users and security researchers to report vulnerabilities in themes and extensions.

2.6 Build and Deployment Processes:

  • Security Implications: The build and deployment processes are critical for ensuring the integrity of the application. A compromised build process could lead to the distribution of a malicious version of the keyboard.
  • Specific Threats:
    • Compromised Build Server: An attacker could gain control of the build server and inject malicious code into the APK.
    • Dependency Hijacking: An attacker could compromise a dependency and inject malicious code.
    • Man-in-the-Middle (MitM) Attacks: An attacker could intercept the APK during download and replace it with a malicious version.
  • Mitigation Strategies:
    • Secure Build Environment: Use a secure build environment with limited access and regular security updates. Consider using a dedicated build server or a trusted CI/CD service (like GitHub Actions, configured securely).
    • Dependency Management: Use a dependency management tool (like Gradle) to track and manage dependencies. Regularly update dependencies to patch known vulnerabilities. Use a Software Bill of Materials (SBOM) to track all components.
    • Code Signing: Digitally sign the APK file to ensure its integrity and authenticity. Use a strong signing key and protect it carefully.
    • Reproducible Builds: Strive for reproducible builds, which allow anyone to verify that the APK was built from the published source code.
    • Secure Distribution: Distribute the APK through trusted channels (e.g., F-Droid, Google Play Store). Use HTTPS for all downloads.

3. Threat Modeling and Prioritization

Based on the component analysis and business risks, here's a prioritized list of threats:

Threat Likelihood Impact Priority
Data Breach (Keystroke Logging) Medium High High
Malicious Code Injection (via Extensions) Medium High High
Privilege Escalation (IME Vulnerability) Low High High
Dependency Hijacking Low High High
IPC Vulnerabilities Medium Medium Medium
Data Leakage (from Logic Component) Medium Medium Medium
Unauthorized Access to Data Storage Medium Medium Medium
Denial of Service (IME Crash) Medium Low Low
UI Redressing/Overlay Attacks Low Low Low

Justification:

  • High Priority: Threats that could lead to a significant data breach (keystroke logging) or compromise the entire device (privilege escalation) are the highest priority. Malicious code injection via extensions is also high priority due to the potential for widespread impact. Dependency hijacking is a low likelihood but high impact event.
  • Medium Priority: Threats that could lead to data leakage or unauthorized access to user data are medium priority.
  • Low Priority: Threats that are primarily mitigated by the Android system or have a limited impact are lower priority.

4. Mitigation Strategies (Actionable and Tailored)

This section provides specific, actionable mitigation strategies, building upon the component-specific recommendations and addressing the prioritized threats.

  1. Keystroke Logging Prevention:

    • Primary Mitigation: Never store raw keystrokes persistently. Process input in memory and discard it immediately after use.
    • Defense in Depth: Implement robust input validation and sanitization throughout the application to prevent injection attacks that could lead to keystroke logging.
    • Android API Review: Carefully review all uses of Android APIs related to text input to ensure they are used securely and do not inadvertently leak keystrokes.

  2. Malicious Code Injection (Extensions) Prevention:

    • Sandboxing: Implement a robust sandboxing mechanism for extensions. This is the most critical mitigation. Explore options like:
      • Separate Processes: Run extensions in separate processes with limited permissions.
      • Restricted Contexts: Use Android's createPackageContext() with CONTEXT_RESTRICTED to create a limited context for extensions.
      • WebView Sandboxing: If extensions use WebViews, use Android's WebView sandboxing features and a strict Content Security Policy (CSP).
    • Permission System: Implement a granular permission system for extensions. Require extensions to declare the permissions they need, and allow users to review and approve these permissions.
    • Code Signing and Verification: Require extensions to be digitally signed. Verify the signature before loading the extension.
    • Static and Dynamic Analysis: Integrate static and dynamic analysis tools into the build process to scan extensions for malicious code.

  3. Privilege Escalation Prevention:

    • Principle of Least Privilege: Request only the minimum necessary permissions in the Android manifest.
    • Secure IPC: Use secure IPC mechanisms and validate all data received from other applications.
    • Regular Security Audits: Conduct regular security audits of the IME's interaction with the Android system.
    • Fuzz Testing: Perform fuzz testing on the IME's interface.

  4. Dependency Hijacking Prevention:

    • Dependency Pinning: Pin dependencies to specific versions to prevent unexpected updates.
    • Vulnerability Scanning: Use a dependency vulnerability scanner (e.g., Dependabot, Snyk) to identify and address known vulnerabilities.
    • SBOM: Maintain a Software Bill of Materials (SBOM) to track all dependencies and their versions.

  5. Data Storage Protection:

    • Encryption at Rest: Encrypt the user dictionary and other sensitive data using a strong encryption algorithm (e.g., AES-256 with GCM).
    • Key Management: Use Android's Keystore system to securely manage encryption keys. Consider using hardware-backed keys if available.
    • Secure File Permissions: Set appropriate file permissions to restrict access to the keyboard's data.

  6. General Security Hardening:

    • Regular Code Reviews: Conduct regular code reviews with a focus on security.
    • Static Analysis (SAST): Integrate SAST tools into the build process.
    • Dynamic Analysis (DAST): Consider using DAST tools to test the running application.
    • Vulnerability Disclosure Program: Establish a clear vulnerability disclosure program.
    • Security Training: Provide security training for developers.

5. Review of Existing Security Controls

  • Open Source Codebase: This is a strong security control, allowing for community scrutiny and audits. However, it doesn't guarantee security; it simply increases the likelihood of vulnerabilities being discovered.
  • Limited Permissions: This is a crucial security control, minimizing the attack surface. It's essential to maintain this principle.
  • No Network Access (Default): This is a very strong security control for a privacy-focused keyboard. It significantly reduces the risk of remote attacks.
  • Local Data Storage: This is generally good for privacy, but it needs to be combined with strong encryption to protect the data.
  • Code Reviews: This is a standard best practice, but its effectiveness depends on the thoroughness of the reviews.

Gaps:

  • Formal Security Audits: The lack of frequent formal security audits is a significant gap.
  • Sandboxing of Extensions: This is a critical gap if extensions are supported.
  • Encryption at Rest: This is a crucial gap if user data is not currently encrypted.
  • Automated Security Testing: While code reviews are mentioned, the lack of explicit mention of automated SAST and DAST is a gap.

6. Addressing Questions and Assumptions

  • Cloud Synchronization: If cloud synchronization is planned, it introduces a major new attack surface. It would require:
    • End-to-End Encryption: Data must be encrypted on the device before being sent to the cloud and decrypted only on the receiving device.
    • Secure Authentication: Robust authentication mechanisms are needed to protect user accounts.
    • Secure Cloud Storage: The cloud storage provider must be carefully vetted and have strong security practices.
    • Transparency: Users must be fully informed about how their data is being synchronized and protected.
  • Vulnerability Disclosure Program: A clear process is essential. This should include:
    • A dedicated email address or reporting channel.
    • A clear scope of what is considered a reportable vulnerability.
    • A commitment to timely response and remediation.
    • Recognition for security researchers who report vulnerabilities.
  • Hardware-Backed Security: Supporting hardware-backed security features (e.g., secure enclaves) would significantly enhance security, especially for key management. This should be considered if feasible.
  • Cryptographic Libraries: Use well-vetted cryptographic libraries (e.g., those provided by Android's security providers or Bouncy Castle). Keep these libraries up-to-date. Avoid implementing custom cryptographic algorithms.
  • Theme/Extension Review: The process should include:
    • Automated Scanning: Use static and dynamic analysis tools.
    • Manual Review: A security expert should review the code of potentially risky extensions.
    • Permission Review: Carefully examine the permissions requested by extensions.
  • Telemetry/Analytics: If any telemetry is collected, it must be:
    • Minimal: Collect only the data that is absolutely necessary.
    • Anonymized: Remove any personally identifiable information (PII).
    • Transparent: Clearly inform users about what data is being collected and how it is being used.
    • Optional: Allow users to opt out of telemetry collection.

The assumptions made in the security design review are generally reasonable. The emphasis on privacy and local data storage is appropriate for a keyboard application. The assumption that formal security audits may be limited is also realistic for many open-source projects. However, it highlights the importance of leveraging community audits and implementing automated security testing.