mitigations.md

Mitigation Strategies Analysis for pallets/jinja

Mitigation Strategy: Autoescaping

Description:

1. Configuration: Modify the Jinja2 Environment initialization to enable autoescaping by default. This is done where the Jinja2 environment is created.
2. Code Modification:

   from jinja2 import Environment, FileSystemLoader, select_autoescape
   
   env = Environment(
       loader=FileSystemLoader('templates'),  # Path to your templates
       autoescape=select_autoescape(['html', 'htm', 'xml']) # Autoescape HTML and XML
   )
   # OR, for simpler cases:
   # env = Environment(loader=FileSystemLoader('templates'), autoescape=True)

3. Verification: After enabling, test with malicious input (e.g., <script>alert('XSS')</script>) in variables. Verify the rendered output contains escaped equivalents (e.g., <script>alert('XSS')</script>).
4. Ongoing Monitoring: Regularly review template rendering and ensure autoescaping isn't accidentally disabled.

• Threats Mitigated:

  • Cross-Site Scripting (XSS) (Severity: High): Prevents injected JavaScript from executing.
  • HTML Injection (Severity: Medium): Prevents injecting arbitrary HTML tags.
  • Template Injection (Severity: High): Reduces the attack surface by preventing common injection forms.

• Impact:

  • XSS: Risk reduction: Very High.
  • HTML Injection: Risk reduction: Very High.
  • Template Injection: Risk reduction: High.

• Currently Implemented:

  • Example: app/config.py (Jinja2 environment initialization).
  • Example: All templates in templates/ are autoescaped.

• Missing Implementation:

  • Example: Verify email templates (templates/email/) are also autoescaped.
  • Example: Check custom template loaders for bypassing autoescaping.

Mitigation Strategy: Explicitly Marking Safe Content

Description:

1. Identify Safe Content: Carefully analyze instances where you render non-user-provided, known-safe HTML.
2. Use MarkupSafe: Wrap safe HTML with MarkupSafe before passing it to the template context.

   from markupsafe import Markup
   
   safe_html = Markup("<strong>This is safe HTML.</strong>")
   context = {'safe_content': safe_html}
   # Pass 'context' to the template

3. Use |safe Filter (Sparingly): In the template, use |safe only on variables marked as safe with MarkupSafe or rigorously validated.

   {{ safe_content | safe }}

4. Document Justification: For every use of |safe or MarkupSafe, add a comment explaining why it's safe.
5. Avoid Overuse: Minimize |safe use. Each instance increases risk if content isn't truly safe.

• Threats Mitigated:

  • XSS (Severity: High): Incorrect |safe use can introduce XSS. Correct use avoids this.
  • HTML Injection (Severity: Medium): Similar to XSS, incorrect use introduces vulnerabilities.

• Impact:

  • XSS: Risk reduction: Neutral (correct use) / Risk increase: Very High (incorrect use).
  • HTML Injection: Risk reduction: Neutral (correct use) / Risk increase: High (incorrect use).

• Currently Implemented:

  • Example: app/utils.py (generate_safe_banner) uses MarkupSafe.
  • Example: templates/home.html uses {{ banner | safe }}.

• Missing Implementation:

  • Example: Review all |safe uses for MarkupSafe or strong justification.
  • Example: Check for user-provided data accidentally marked as safe.

Mitigation Strategy: Sandboxing (For Untrusted Templates)

Description:

1. Identify Untrusted Templates: Determine if users can upload or create templates (untrusted).
2. Use SandboxedEnvironment: Create a separate Jinja2 environment using SandboxedEnvironment for untrusted templates.

   from jinja2 import SandboxedEnvironment, FileSystemLoader
   
   sandboxed_env = SandboxedEnvironment(loader=FileSystemLoader('untrusted_templates'))

3. Load Untrusted Templates: Use sandboxed_env to load and render from the untrusted source.

   template = sandboxed_env.from_string(untrusted_template_string)
   rendered_output = template.render(context)

4. Configure Restrictions: Review and customize SandboxedEnvironment restrictions if needed.
5. Testing: Thoroughly test with malicious template inputs.

• Threats Mitigated:

  • Remote Code Execution (RCE) (Severity: Critical): Prevents access to Python built-ins and dangerous functions.
  • Information Disclosure (Severity: High): Restricts access to sensitive attributes/methods.
  • Template Injection (Severity: High): Strong defense against template injection.

• Impact:

  • RCE: Risk reduction: Very High.
  • Information Disclosure: Risk reduction: High.
  • Template Injection: Risk reduction: High.

• Currently Implemented:

  • Example: app/views/user_templates.py uses SandboxedEnvironment.

• Missing Implementation:

  • Example: Migrate any other untrusted template rendering to SandboxedEnvironment.

Mitigation Strategy: Template Design Best Practices (Jinja2 Specific)

Description:

1. Minimize Logic: Keep templates focused on presentation. Avoid complex logic in templates. Do it in application code.
2. Use Template Inheritance: Create a base template (base.html) with common elements. Use {% extends %} and {% block %}.
3. Separate Data and Presentation: Clearly separate data (context) from presentation logic.
4. Use Included Templates: For reusable snippets, use {% include %}.
5. Avoid Dynamic Includes: Crucially, avoid using variables to determine which template to include (e.g., {% include user_selected_template %}). This is a major Jinja2-specific risk.

• Threats Mitigated:

  • Template Injection (Severity: High): Simplifying templates and avoiding dynamic includes reduces the attack surface.
  • Information Disclosure (Severity: Medium): Avoiding complex logic reduces accidental exposure.

• Impact:

  • Template Injection: Risk reduction: Medium (especially avoiding dynamic includes).
  • Information Disclosure: Risk reduction: Low.

• Currently Implemented:

  • Example: templates/base.html is the base template.
  • Example: Templates use {% extends 'base.html' %}.

• Missing Implementation:

  • Example: Refactor old templates with excessive logic.
  • Example: Ensure consistent inheritance.
  • Example: Remove any dynamic includes. This is the most important part of this strategy.

Mitigation Strategy: Avoid eval and exec like functionality within Custom Filters/Functions

Description:

1. Review Custom Filters and Functions: Examine any custom Jinja2 filters or functions. Ensure none dynamically execute code based on user input.
2. Avoid Dynamic Code Generation: Do not create filters/functions that take user input to construct and execute Python code.
3. Use Safe Alternatives: Use Jinja2's built-in filters and tests for common tasks.
4. Sandboxing (If Absolutely Necessary): If you must use dynamic code execution, heavily restrict and sandbox it. Use an isolated environment. Thoroughly validate input. Highly discouraged.
5. Documentation and Review: Document custom filters/functions, stating purpose and security. Regularly review.

• Threats Mitigated:

  • Remote Code Execution (RCE) (Severity: Critical): Prevents injecting and executing arbitrary Python.
  • Template Injection (Severity: High): Reduces the attack surface.

• Impact:

  • RCE: Risk reduction: Very High.
  • Template Injection: Risk reduction: High.

• Currently Implemented:

  • Example: Code review guidelines prohibit eval/exec in custom Jinja2 components.

• Missing Implementation:

  • Example: Thoroughly review existing custom filters/functions.
  • Example: Implement automated checks for eval/exec.