mitigations.md

Mitigation Strategies Analysis for github/markup

Mitigation Strategy: Strict Input Validation (Before github/markup)

1. Strict Input Validation (Before github/markup)

• Mitigation Strategy: Strict Allowlist-Based Input Validation

• Description:

  1. Define Allowed Markup: Create a precise definition of exactly what markup elements and attributes are permitted. This should be an allowlist, not a denylist. For example, if only basic Markdown is needed (bold, italics, links, lists), define this explicitly.
  2. Develop Validation Logic: Implement validation logic (e.g., using regular expressions, a dedicated parsing library, or a combination) that strictly enforces the allowlist. This logic should be applied before any data is passed to github/markup.
  3. Reject Invalid Input: If the input does not exactly match the allowed pattern, reject it outright. Do not attempt to "sanitize" or modify the input. Return a clear error message to the user.
  4. Contextual Validation: Consider the context of the input. If a field should only contain a single line of text, reject input containing newlines or HTML tags.
  5. Example (Conceptual Python):

     import re
     
     ALLOWED_MARKDOWN = re.compile(r"^(?:[a-zA-Z0-9\s]+|\*(?:[a-zA-Z0-9\s]+)\*|_(?:[a-zA-Z0-9\s]+)_|(?:\\[[^\\]]+\\]\\([^)]+\\)))$")  # Very basic example
     
     def validate_markdown(input_text):
         if ALLOWED_MARKDOWN.match(input_text):
             return True
         else:
             return False
     
     user_input = get_user_input()
     if validate_markdown(user_input):
         # Process with github/markup
         pass
     else:
         # Reject input
         display_error("Invalid input format.")

• List of Threats Mitigated:

  • Cross-Site Scripting (XSS): (Severity: High) - Prevents malicious JavaScript from being injected via crafted markup.
  • HTML Injection: (Severity: High) - Prevents arbitrary HTML from being injected, which could be used to deface the site or steal user data.
  • Some Denial-of-Service (DoS) Vectors: (Severity: Medium) - By limiting the complexity of allowed markup, reduces the risk of overly complex input causing excessive processing.

• Impact:

  • XSS: Significantly reduces the risk. If the allowlist is correctly implemented, XSS via markup injection becomes extremely difficult.
  • HTML Injection: Similar to XSS, significantly reduces the risk.
  • DoS: Provides some protection, but other DoS-specific mitigations are still needed.

• Currently Implemented:

  • Specify where in your project this is implemented (e.g., "Implemented in the comments module, validate_comment function"). If partially implemented, describe the current state. Example: "Partially implemented. Basic length checks are in place, but a full allowlist is not yet defined."

• Missing Implementation:

  • Specify where this is not implemented (e.g., "Not implemented for user profile descriptions," or "Allowlist is too broad and needs refinement"). Example: "Missing a comprehensive allowlist for all user-input fields. Currently relying on renderer-level sanitization, which is insufficient."

Mitigation Strategy: Leverage Underlying Renderers' Security Features

2. Leverage Underlying Renderers' Security Features

• Mitigation Strategy: Configure Underlying Renderers Securely

• Description:

  1. Identify Renderers: Determine which rendering libraries github/markup is using for the supported markup formats (e.g., python-markdown, asciidoctor, docutils).
  2. Research Security Options: For each renderer, thoroughly research its security-related configuration options. Consult the official documentation.
  3. Implement Secure Settings: Apply the most restrictive security settings that are compatible with your application's requirements. This often involves:
     • Markdown: Using html_replacement_text in python-markdown and integrating bleach with a strict allowlist of tags and attributes.
     • AsciiDoc: Using Asciidoctor's safe mode (preferably secure mode).
     • reStructuredText: Setting Docutils' security_level and disabling raw_enabled.
  4. Configuration Files: Store these security settings in configuration files that are managed separately from the application code.
  5. Testing: Thoroughly test the configuration to ensure it's working as expected and doesn't break legitimate functionality.

• List of Threats Mitigated:

  • Cross-Site Scripting (XSS): (Severity: High) - Reduces the risk of XSS by leveraging the renderer's built-in sanitization capabilities.
  • HTML Injection: (Severity: High) - Similar to XSS.
  • File Inclusion (Specific Renderers): (Severity: Medium) - Prevents unauthorized access to local files or external resources through directives like include in reStructuredText.

• Impact:

  • XSS/HTML Injection: Provides a significant layer of defense, but should not be relied upon as the sole mitigation. Input validation is still crucial.
  • File Inclusion: Effectively mitigates this threat if configured correctly.

• Currently Implemented:

  • Specify which renderers are configured securely and where (e.g., "Markdown renderer is configured with bleach in markup_processing.py. Asciidoctor is set to safe mode.").

• Missing Implementation:

  • Specify which renderers are not configured securely or where the configuration is incomplete (e.g., "reStructuredText renderer is not yet configured with security settings," or "Bleach allowlist needs to be reviewed and tightened").

Mitigation Strategy: Input Length Limits

3. Input Length Limits

• Mitigation Strategy: Impose Strict Input Length Limits

• Description:

  1. Determine Reasonable Limits: Based on the intended use of each input field, determine reasonable maximum lengths for user-supplied markup. Consider the context (e.g., a comment field vs. a document editor).
  2. Enforce Limits Early: Enforce these limits before the input is passed to github/markup. This prevents unnecessarily processing large inputs.
  3. Client-Side and Server-Side: Implement length limits both on the client-side (using HTML attributes like maxlength or JavaScript) and on the server-side. Client-side checks can improve the user experience, but server-side checks are essential for security.
  4. Clear Error Messages: Provide clear error messages to the user if the input exceeds the allowed length.

• List of Threats Mitigated:

  • Denial of Service (DoS): (Severity: Medium) - Reduces the risk of overly long input causing excessive processing time or memory consumption.

• Impact:

  • DoS: Provides a basic level of protection against simple DoS attacks based on input length.

• Currently Implemented:

  • Specify where length limits are enforced (e.g., "maxlength attribute is used on comment forms," or "Server-side length validation is implemented in the process_input function").

• Missing Implementation:

  • Specify where length limits are missing or need to be adjusted (e.g., "No length limits are enforced for user profile descriptions," or "Length limits need to be reviewed and potentially lowered").

Mitigation Strategy: Resource Limits (Renderer-Specific)

4. Resource Limits (Renderer-Specific)

• Mitigation Strategy: Configure Renderer-Specific Resource Limits

• Description:

  1. Research Renderer Options: Examine the documentation of each underlying rendering library used by github/markup to identify any options related to resource limits (e.g., memory usage, recursion depth, processing time).
  2. Apply Limits: Configure these limits to reasonable values that prevent excessive resource consumption. This may involve setting limits on nested lists, table sizes, or other complex markup structures.
  3. Testing: Test the configuration to ensure it doesn't negatively impact legitimate use cases.

• List of Threats Mitigated:

  • Denial of Service (DoS): (Severity: Medium) - Reduces the risk of DoS attacks that exploit specific features of the rendering libraries.

• Impact:

  • DoS: Provides protection against more sophisticated DoS attacks that target the rendering process.

• Currently Implemented:

  • Specify which renderers have resource limits configured and where (e.g., "Markdown renderer has a limit on nested list depth," or "No resource limits are currently configured for any renderers").

• Missing Implementation:

  • Specify which renderers lack resource limits or where the configuration needs to be reviewed (e.g., "Need to investigate resource limit options for the AsciiDoc renderer").

Mitigation Strategy: Timeout for Markup Processing

5. Timeout for Markup Processing

• Mitigation Strategy: Implement Timeout for Markup Processing

• Description:

  1. Wrap github/markup Call: Wrap the call to github/markup.render (or equivalent function) with a timeout mechanism. This can be achieved using libraries like timeout-decorator in Python or similar constructs in other languages.
  2. Set Reasonable Timeout: Determine a reasonable timeout value based on the expected processing time for typical input. This value should be long enough to allow legitimate rendering but short enough to prevent long-running processes.
  3. Handle Timeout Exception: Implement proper exception handling to gracefully handle timeout exceptions. This might involve returning an error message to the user or logging the event.
  4. Example (Conceptual Python with timeout-decorator):

  from timeout_decorator import timeout, TimeoutError
  import github.markup
  
  @timeout(5)  # 5-second timeout
  def render_markup_with_timeout(filename, content):
      try:
          return github.markup.render(filename, content)
      except TimeoutError:
          # Handle timeout (e.g., log, return error)
          print(f"Markup rendering timed out for {filename}")
          return None
  
  # ... elsewhere in your code ...
  rendered_html = render_markup_with_timeout("user_input.md", user_content)
  if rendered_html is None:
      # Display error to user
      pass

• List of Threats Mitigated:

  • Denial of Service (DoS): (Severity: Medium) - Prevents long-running markup processing from blocking the application or consuming excessive resources.

• Impact:

  • DoS: Significantly reduces the risk of DoS attacks that rely on slow or infinite processing.

• Currently Implemented:

  • Specify where the timeout is implemented (e.g., "Timeout implemented in the render_content function using the timeout library").

• Missing Implementation:

  • Specify where the timeout is missing (e.g., "No timeout is currently implemented for markup processing").

Mitigation Strategy: Restrict File Access (Renderer-Specific)

6. Restrict File Access (Renderer-Specific)

• Mitigation Strategy: Disable File Inclusion Features

• Description:

  1. Identify Potentially Dangerous Directives: Research the documentation of each rendering library to identify any features that allow including external files or accessing system resources (e.g., the include directive in reStructuredText).
  2. Disable or Restrict: Disable these features completely if they are not essential. If they are required, restrict their usage as much as possible (e.g., by limiting the allowed paths or file types).
  3. Configuration: Implement these restrictions through the renderer's configuration options.

• List of Threats Mitigated:

  • Information Disclosure: (Severity: High) - Prevents attackers from accessing sensitive files on the server.
  • Remote Code Execution (RCE): (Severity: Critical) - In some cases, file inclusion vulnerabilities can lead to RCE.

• Impact:

  • Information Disclosure/RCE: Effectively mitigates these threats if configured correctly.

• Currently Implemented:

  • Specify which renderers have file access restrictions and where (e.g., "reStructuredText renderer has raw_enabled set to false and file_insertion_enabled set to false").

• Missing Implementation:

  • Specify which renderers lack file access restrictions or where the configuration needs to be reviewed (e.g., "Need to verify that all renderers have file inclusion features disabled").

This revised list focuses solely on mitigations that directly interact with the markup input and the rendering process itself. This provides a more targeted approach to securing the github/markup integration.