mitigations.md

Mitigation Strategies Analysis for pallets/jinja

Mitigation Strategy: Utilize Jinja's Sandboxed Environment

• Description:

  • Step 1: Import SandboxedEnvironment from jinja2.sandbox.
  • Step 2: Instantiate SandboxedEnvironment instead of Environment when creating your Jinja environment.

    from jinja2.sandbox import SandboxedEnvironment
    
    # Instead of:
    # env = Environment(loader=...)
    
    env = SandboxedEnvironment(loader=...)

  • Step 3: Review the default restrictions of SandboxedEnvironment. It restricts access to:
    • __import__ function
    • getattr and setattr built-in functions
    • globals and locals
    • eval and exec
    • File system access
  • Step 4: If necessary, customize the SandboxedEnvironment by modifying allowed_filters, allowed_tests, and allowed_attributes to permit specific functionalities required by your application while maintaining security. Be very cautious when adding to these lists.
  • Step 5: Ensure all template rendering uses this SandboxedEnvironment instance.

• Threats Mitigated:

  • Server-Side Template Injection (SSTI) (Severity: High) - Attackers can execute arbitrary code on the server.

• Impact:

  • Server-Side Template Injection (SSTI): High Risk Reduction - Significantly reduces the attack surface for SSTI by limiting access to dangerous functionalities.

• Currently Implemented:

  • Status: Not Implemented
  • Location: N/A

• Missing Implementation:

  • Location: Everywhere Jinja Environment is instantiated for template rendering across the application. This includes template rendering in web views, background tasks that use templates, and any other place where Jinja templates are processed.

Mitigation Strategy: Strictly Control Template Context

• Description:

  • Step 1: Review all code sections where data is passed to the Jinja template context (e.g., in view functions before rendering templates).
  • Step 2: Identify the absolute minimum data required for each template to function correctly.
  • Step 3: Remove any unnecessary variables from the template context.
  • Step 4: Avoid passing entire objects or complex data structures directly. Instead, pass only the specific attributes or processed data needed by the template.
  • Step 5: Sanitize and validate all data before adding it to the template context, even if it originates from internal sources. Treat all data as potentially untrusted.
  • Step 6: Regularly review the template context data to ensure no accidental or unnecessary data exposure occurs.

• Threats Mitigated:

  • Server-Side Template Injection (SSTI) (Severity: High) - Reduces the potential attack surface by limiting exploitable objects and data in the template context.
  • Information Disclosure (Severity: Medium) - Prevents accidental exposure of sensitive data that might be present in objects passed to the template.

• Impact:

  • Server-Side Template Injection (SSTI): Medium Risk Reduction - Makes SSTI exploitation harder by limiting available tools and information.
  • Information Disclosure: Medium Risk Reduction - Reduces the chance of unintentionally leaking sensitive data through templates.

• Currently Implemented:

  • Status: Partially Implemented
  • Location: In some newer modules, context data is minimized, but older modules might pass more data than necessary.

• Missing Implementation:

  • Location: All existing view functions and template rendering logic, especially in older modules. Requires a systematic review of all template context creation points.

Mitigation Strategy: Disable or Restrict Dangerous Jinja Features (If Possible and Applicable)

• Description:

  • Step 1: Analyze your application's Jinja template usage to identify if any potentially dangerous features like filters, tests, or global functions are actually required.
  • Step 2: If certain features are not essential, disable them in your Jinja environment configuration.
    • For example, to remove a specific filter:

      env = Environment(loader=...)
      del env.filters['filter_name']

    • To restrict access to global functions, you might need to customize the SandboxedEnvironment further or create a custom environment.
  • Step 3: If complete disabling is not possible, consider restricting the usage of dangerous features to only trusted templates or contexts.
  • Step 4: Document any disabled or restricted features and the rationale behind it.

• Threats Mitigated:

  • Server-Side Template Injection (SSTI) (Severity: High) - Removes potential attack vectors by eliminating or limiting access to exploitable features.

• Impact:

  • Server-Side Template Injection (SSTI): Medium Risk Reduction - Reduces the attack surface by removing potentially dangerous tools available to attackers.

• Currently Implemented:

  • Status: Not Implemented
  • Location: N/A - Default Jinja environment is used without feature restrictions.

• Missing Implementation:

  • Location: Jinja environment configuration. Requires analysis of template usage to determine which features can be safely disabled or restricted without breaking application functionality.

Mitigation Strategy: Enforce Jinja's Auto-Escaping

• Description:

  • Step 1: Verify that auto-escaping is enabled in your Jinja environment configuration. By default, Jinja auto-escaping is enabled for HTML and XML contexts.
  • Step 2: Ensure that auto-escaping is configured for the correct context (e.g., html, xml, xhtml, javascript, css, url). You can configure default auto-escaping or specify it per template.
  • Step 3: If you are using custom Jinja environments, explicitly enable auto-escaping during environment creation:

    env = Environment(loader=..., autoescape=True) # Enable for HTML, XML, XHTML
    # or
    env = Environment(loader=..., autoescape=select_autoescape(['html', 'xml'])) # More specific

  • Step 4: Be extremely cautious when using the safe filter or Markup objects to bypass auto-escaping. Only use these when you are absolutely certain the data is safe and has been properly sanitized outside of Jinja.
  • Step 5: Regularly review templates to ensure auto-escaping is consistently applied and not bypassed unnecessarily.

• Threats Mitigated:

  • Cross-Site Scripting (XSS) (Severity: High) - Prevents XSS vulnerabilities by automatically escaping potentially harmful characters in user-provided data rendered in templates.

• Impact:

  • Cross-Site Scripting (XSS): High Risk Reduction - Significantly reduces the risk of XSS by automatically handling escaping in most common contexts.

• Currently Implemented:

  • Status: Implemented
  • Location: Auto-escaping is enabled in the main Jinja environment configuration.

• Missing Implementation:

  • Location: While enabled, a review is needed to ensure consistent application across all templates and to verify that safe filter and Markup are used judiciously and safely.

Mitigation Strategy: Context-Aware Escaping When Disabling Auto-Escaping

• Description:

  • Step 1: Avoid disabling auto-escaping unless absolutely necessary. Re-evaluate the need to disable it and explore alternative solutions that allow auto-escaping to remain enabled.
  • Step 2: If you must disable auto-escaping for specific sections or templates, implement context-aware escaping manually.
  • Step 3: Use Jinja's built-in escaping filters (escape or e) explicitly to escape data based on the context where it will be rendered.
    • For HTML context: {{ user_input | e }} or {{ user_input | escape }}
    • For JavaScript context (JSON encoding is often better): {{ user_input | tojson | safe }} (use safe cautiously after proper encoding)
    • For URL context: {{ url | urlencode }}
  • Step 4: Clearly document in the template code and in development guidelines why auto-escaping is disabled and how manual escaping is implemented.
  • Step 5: Regularly review templates where auto-escaping is disabled to ensure manual escaping is correctly and consistently applied.

• Threats Mitigated:

  • Cross-Site Scripting (XSS) (Severity: High) - Prevents XSS vulnerabilities when auto-escaping is intentionally disabled by ensuring manual escaping is correctly implemented.

• Impact:

  • Cross-Site Scripting (XSS): High Risk Reduction - Maintains a high level of XSS protection even when auto-escaping is disabled in specific cases, if manual escaping is done correctly. (Note: Manual escaping is more error-prone than auto-escaping).

• Currently Implemented:

  • Status: Partially Implemented
  • Location: In some templates where raw HTML rendering is required, auto-escaping might be disabled, but manual escaping might not be consistently applied or context-aware.

• Missing Implementation:

  • Location: Review all templates where auto-escaping is disabled. Implement context-aware manual escaping using Jinja's escaping filters. Create guidelines for developers on when and how to disable auto-escaping and implement manual escaping.

Mitigation Strategy: Avoid Rendering User-Provided Data Directly in JavaScript Contexts

• Description:

  • Step 1: Minimize rendering user-provided data directly within <script> tags or JavaScript event handlers in Jinja templates.
  • Step 2: If you must include user-provided data in JavaScript, use secure methods like JSON encoding to serialize the data and then parse it in JavaScript.

    <script>
        var userData = {{ user_data | tojson | safe }}; // Use tojson and then safe cautiously
        // ... use userData in JavaScript ...
    </script>

  • Step 3: Avoid directly embedding user input into strings within JavaScript code.
  • Step 4: If you need to dynamically generate JavaScript code based on user input (which should be rare), carefully sanitize and validate the input before embedding it in the JavaScript string. Consider using templating libraries within JavaScript itself if complex dynamic JavaScript generation is needed.
  • Step 5: Prefer passing data to JavaScript through data attributes on HTML elements and accessing them via JavaScript, rather than directly embedding data in <script> blocks.

• Threats Mitigated:

  • Cross-Site Scripting (XSS) (Severity: High) - Prevents XSS vulnerabilities that are particularly dangerous when user input is directly injected into JavaScript code.

• Impact:

  • Cross-Site Scripting (XSS): High Risk Reduction - Significantly reduces the risk of JavaScript-context XSS, which can be very impactful.

• Currently Implemented:

  • Status: Partially Implemented
  • Location: In some areas, user data is passed to JavaScript using tojson, but direct string embedding might still exist in older parts of the application.

• Missing Implementation:

  • Location: Review all templates that render data within <script> tags or JavaScript event handlers. Refactor to use tojson for data serialization and avoid direct string embedding. Establish guidelines to prevent direct embedding in JavaScript contexts in the future.

Mitigation Strategy: Careful Error Handling in Templates

• Description:

  • Step 1: Configure Jinja to use a generic error handler in production environments. Avoid displaying detailed error messages or stack traces directly to users.
  • Step 2: Implement custom error pages that provide user-friendly error messages without revealing sensitive internal application details.
  • Step 3: Log detailed error information (including stack traces) securely to server logs for debugging and monitoring purposes. Ensure these logs are not publicly accessible.
  • Step 4: In development and staging environments, you can enable more verbose error reporting to aid in debugging, but ensure this is disabled in production.
  • Step 5: Review template error handling logic to ensure it does not inadvertently leak sensitive information.

• Threats Mitigated:

  • Information Disclosure (Severity: Low) - Prevents leakage of sensitive information through detailed error messages displayed in production.

• Impact:

  • Information Disclosure: Low Risk Reduction - Reduces the chance of information leakage through error messages.

• Currently Implemented:

  • Status: Partially Implemented
  • Location: Generic error pages are in place, but the level of detail in error logging and potential information leakage in error messages needs review.

• Missing Implementation:

  • Location: Review and refine error handling configuration for Jinja templates, especially in production. Ensure detailed error logging is secure and error messages displayed to users are generic and non-revealing.