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Mitigation Strategies Analysis for standardnotes/app

Mitigation Strategy: Extension Sandboxing (App-Centric)

Mitigation Strategy: Strict Extension Sandboxing

  • Description:

    1. Isolate Extension Execution: Use Web Workers (for the web app), separate processes (for the desktop app), and platform-specific sandboxing APIs (for mobile apps) to run each extension in a completely isolated environment. This prevents direct access to the main application's memory, DOM (in the web app), or other system resources.
    2. Define a Strict API: Create a well-defined, minimal API for extensions to interact with the core application. This API should be the only way for extensions to access data or functionality. Design the API with the principle of least privilege.
    3. Implement Message Passing: Use a message-passing system (e.g., postMessage for Web Workers) for all communication between the extension and the core application. This enforces a clear boundary and prevents direct function calls or memory access.
    4. Enforce Permissions: Extensions must declare the permissions they require (e.g., "read notes," "modify notes," "access specific note types"). The application should prompt the user to grant these permissions before installation. The application's runtime must enforce these permissions, preventing extensions from exceeding their declared capabilities.
    5. Content Security Policy (CSP): Apply a strict, extension-specific CSP to each extension. This CSP should limit the extension's ability to load external resources (scripts, stylesheets, images) or connect to external servers, even more strictly than the main application's CSP.
    6. Runtime Monitoring: Monitor extensions' resource usage (CPU, memory, network) and API calls within the application. Detect and respond to anomalous behavior (e.g., excessive network requests, attempts to access unauthorized resources) by alerting the user or disabling the extension.

  • Threats Mitigated:

    • Malicious Extensions (Severity: Critical): Prevents extensions from stealing user data, encryption keys, or modifying notes without authorization.
    • Compromised Legitimate Extensions (Severity: Critical): Limits the damage a compromised extension can do by restricting its access.
    • Cross-Site Scripting (XSS) within Extensions (Severity: High): The CSP and isolation help prevent XSS attacks from affecting the main application.
    • Data Exfiltration (Severity: High): Limits the ability of extensions to send user data to external servers.
    • Privilege Escalation (Severity: High): Prevents extensions from gaining unauthorized access to system resources or the core application's functionality.

  • Impact:

    • Malicious Extensions: Risk significantly reduced. An extension can only access data explicitly provided to it via the controlled API.
    • Compromised Extensions: Damage is contained to the extension's sandbox.
    • XSS: Significantly reduced within the extension context.
    • Data Exfiltration: Greatly reduced, as network access is controlled by the CSP and permissions.
    • Privilege Escalation: Effectively prevented.

  • Currently Implemented:

    • Standard Notes does use sandboxing to some extent, particularly with Web Workers for the web application. The extent and consistency of sandboxing across desktop and mobile platforms are less clear from public documentation. They have a permissions system, but its granularity and enforcement strength need further investigation. CSP is likely used, but its strictness and specificity for extensions need verification.

  • Missing Implementation:

    • Comprehensive Sandboxing Across All Platforms: Ensure consistent, robust sandboxing on all platforms (web, desktop, mobile). This requires platform-specific implementations and rigorous testing.
    • Stricter Permission Enforcement: The permission system should be as granular as possible, and enforcement should be rigorously tested at runtime.
    • Dedicated Extension CSP: A dedicated, stricter CSP specifically for extensions is crucial.
    • Runtime Monitoring: Implement comprehensive runtime monitoring of extension behavior within the application.
    • Formal API Documentation: Clear, comprehensive documentation of the extension API, including all available functions, their security implications, and permission requirements.

Mitigation Strategy: Secure Key Storage (App-Centric)

Mitigation Strategy: Secure Key Storage (Client-Side)

  • Description:

    1. Platform-Specific Secure Storage:
      • Desktop: Utilize the operating system's secure credential storage (Keychain on macOS, Credential Manager on Windows, Keyring on Linux) from within the application code.
      • Mobile: Use the platform's secure enclave or keystore (Android Keystore, iOS Keychain) through the application's native components.
      • Web: Never store the master password or unencrypted keys persistently (e.g., in local storage or cookies). Derive encryption keys only in memory, and only for the duration of the active session. Use the Web Crypto API for all cryptographic operations. Clear keys from memory immediately after use.
    2. Limited Key Lifetime: Minimize the time that unencrypted keys exist in the application's memory. Derive keys only when necessary and clear them immediately after use (using secure memory wiping techniques where possible).
    3. Secure Random Number Generation: Use a cryptographically secure random number generator (CSPRNG) provided by the platform or a well-vetted library within the application for all key generation and salt creation.

  • Threats Mitigated:

    • Key Compromise from Disk (Severity: Critical): Protects keys from being stolen if the device is compromised or the hard drive is accessed (relevant to desktop and mobile).
    • Key Compromise from Memory (Severity: High): Reduces the window of opportunity for attackers to extract keys from the application's memory.
    • Unauthorized Access to Keys (Severity: Critical): Prevents unauthorized applications or processes from accessing the stored keys (relevant to desktop and mobile).
    • Key Recovery Attacks (Severity: High): Makes it more difficult for attackers to recover keys using specialized hardware or software.

  • Impact:

    • Key Compromise from Disk/Memory: Risk significantly reduced, especially on desktop and mobile platforms with hardware-backed security.
    • Unauthorized Access: Effectively prevented, assuming the platform's secure storage is properly implemented and accessed correctly by the application.
    • Key Recovery: Increases the difficulty and cost of key recovery attacks.

  • Currently Implemented:

    • Standard Notes likely uses platform-specific secure storage on desktop and mobile, accessing these features from within the application code. The web application's approach to key management (in-memory derivation) is generally sound.

  • Missing Implementation:

    • Formal Security Audit of Key Storage: Conduct a thorough security audit of the key storage implementation within the application code on all platforms.
    • Detailed Documentation: Provide clear documentation on how keys are stored and protected on each platform, specifically detailing the application's interaction with the platform's secure storage mechanisms.
    • Web - Robust Session Management: Ensure robust session management for the web application, with short session timeouts and secure cookie handling (HttpOnly, Secure flags) implemented within the application.
    • Secure memory wiping: Use techniques to securely wipe memory after using sensitive data.

Mitigation Strategy: Client-Side Data Handling

Mitigation Strategy: Secure Client-Side Data Handling

  • Description:

    1. Secure Temporary File Handling (if applicable):
      • If the application uses temporary files, ensure they are created in a secure, temporary directory with appropriate permissions (restricted to the application).
      • Encrypt the contents of temporary files within the application using keys derived from the user's master password.
      • Delete temporary files securely (e.g., using secure deletion utilities or platform-specific APIs) from within the application as soon as they are no longer needed.
    2. Clipboard Protection:
      • Avoid automatically copying sensitive data (e.g., decrypted note content, encryption keys) to the system clipboard.
      • If data must be copied to the clipboard, clear it after a short, configurable timeout from within the application.
      • Provide a user-configurable option to disable clipboard integration entirely.
    3. Memory Protection:
      • Minimize the amount of time that sensitive data (e.g., unencrypted notes, encryption keys) resides in the application's memory.
      • Use memory protection techniques provided by the platform or language (e.g., memory encryption, secure enclaves, if available and practical) within the application.
      • Overwrite sensitive data in memory with zeros or random data before releasing the memory (secure wiping).

  • Threats Mitigated:

    • Data Leakage through Temporary Files (Severity: High): Prevents unauthorized access to sensitive data stored in temporary files.
    • Data Leakage through Clipboard (Severity: Medium): Reduces the risk of sensitive data being exposed through the clipboard.
    • Data Leakage from Memory (Severity: High): Minimizes the window of opportunity for attackers to extract sensitive data from the application's memory.

  • Impact:

    • Temporary File Leakage: Risk significantly reduced if temporary files are encrypted and securely deleted.
    • Clipboard Leakage: Risk reduced, especially with short timeouts and a disable option.
    • Memory Leakage: Risk reduced, although complete prevention is difficult without specialized hardware.

  • Currently Implemented:

    • The extent to which Standard Notes implements these measures is not fully clear from public documentation. Some clipboard management is likely present.

  • Missing Implementation:

    • Comprehensive Review of Data Handling: Conduct a thorough review of how the application handles sensitive data in memory, temporary files, and the clipboard on all platforms.
    • Secure Deletion of Temporary Files: Ensure secure deletion is implemented consistently.
    • Configurable Clipboard Timeout: Provide a user-configurable timeout for clearing the clipboard.
    • Memory Wiping: Implement secure memory wiping techniques where feasible.
    • Documentation: Clearly document the application's data handling practices.