mitigations.md

Mitigation Strategies Analysis for shopify/liquid

Mitigation Strategy: 1. Context-Aware Output Encoding in Liquid Templates

1. Context-Aware Output Encoding in Liquid Templates

• Mitigation Strategy: Context-Aware Output Encoding in Liquid Templates

• Description:

  1. Identify Output Contexts: Within each Liquid template, determine the context where dynamic data is being output (e.g., HTML body, HTML attributes, URLs, JavaScript, CSS).
  2. Apply Liquid Encoding Filters: Consistently use Liquid's built-in encoding filters based on the identified output context within the Liquid template code itself.
     • HTML Context: Use escape or h filters for outputting data within HTML tags or attributes to prevent HTML injection. Example: {{ user_name | escape }}.
     • URL Context: Use url_encode filter when embedding data in URLs to prevent URL injection. Example: <a href="/profile?name={{ user_name | url_encode }}">.
     • JavaScript Context: Use json filter when passing data to JavaScript code within templates to prevent JavaScript injection. Example: <script>var userName = {{ user_name | json }};</script>.
     • CSS Context: Be extremely cautious about using user input in CSS. If absolutely necessary, use CSS-specific escaping or avoid user input in CSS altogether. Liquid itself doesn't have CSS-specific escaping, so this might require custom filters or backend pre-processing before passing to Liquid.
  3. Template Review for Encoding: During template development and review, explicitly check for the correct and consistent application of output encoding filters in all relevant locations within Liquid templates.

• Threats Mitigated:

  • Cross-Site Scripting (XSS): High Severity. Lack of output encoding in HTML context allows attackers to inject malicious scripts that execute in users' browsers. Liquid's escape filter directly mitigates this.
  • URL Injection: Medium Severity. Improper encoding in URLs can lead to users being redirected to malicious sites or manipulated into performing unintended actions. Liquid's url_encode filter mitigates this.
  • JavaScript Injection: Medium Severity. Incorrect handling of data passed to JavaScript can lead to malicious script execution within the page. Liquid's json filter helps mitigate this.

• Impact:

  • XSS: High Risk Reduction. Context-aware output encoding using Liquid filters is a primary defense against XSS within templates.
  • URL Injection: Medium Risk Reduction. Liquid's url_encode effectively prevents URL injection when used correctly.
  • JavaScript Injection: Medium Risk Reduction. Liquid's json filter provides a safe way to pass data to JavaScript.

• Currently Implemented:

  • Output Encoding: Partially implemented in some templates using escape filter for user names displayed in HTML.

• Missing Implementation:

  • Consistent Output Encoding: Inconsistent use of output encoding filters across all templates. Missing url_encode for URLs and json for JavaScript contexts within Liquid templates. No specific CSS context handling within Liquid templates (requires external handling if needed).
  • Template Review for Encoding: No formal process for specifically reviewing Liquid templates to ensure consistent and correct output encoding.

Mitigation Strategy: 2. Restrict Liquid Functionality and Features in Configuration

2. Restrict Liquid Functionality and Features in Configuration

• Mitigation Strategy: Restrict Liquid Functionality and Features via Configuration

• Description:

  1. Identify Unnecessary Liquid Features: Analyze the application's Liquid templates and identify which Liquid tags and filters are actually necessary for the application's functionality. Focus on potentially dangerous tags like render, include, layout, and custom filters.
  2. Configure Liquid Engine to Restrict Features: Utilize the Liquid engine's configuration options to disable or restrict the use of unnecessary or potentially dangerous tags and filters.
     • Configuration Options: Consult the specific Liquid engine implementation's documentation (e.g., Shopify Liquid, Ruby Liquid, etc.) for configuration options to disable specific tags and filters. This might involve setting configuration flags or providing a list of allowed/disallowed features during engine initialization.
     • Example (Conceptual): If render, include, and layout tags are not used, configure the Liquid engine to disallow these tags. Similarly, if custom filters are not needed, prevent their registration in the Liquid engine setup.
  3. Regular Configuration Review: Periodically review the Liquid engine configuration to ensure that restrictions are still appropriate and effective, and to adapt to any changes in application requirements or identified threats.

• Threats Mitigated:

  • Server-Side Template Injection (SSTI): High Severity. Restricting powerful Liquid features directly reduces the attack surface for SSTI by limiting the capabilities available to an attacker even if they can inject Liquid code.
  • Remote Code Execution (RCE): High Severity (subset of SSTI). Disabling dangerous tags like render and include in Liquid configuration can prevent attackers from using these tags to include and potentially execute arbitrary code (depending on the specific Liquid implementation and environment).
  • Information Disclosure: Medium Severity. Limiting Liquid features can prevent attackers from using template features to access and exfiltrate sensitive data if they manage to inject Liquid code.

• Impact:

  • SSTI: Medium to High Risk Reduction. Significantly reduces the attack surface and potential for exploitation by limiting available Liquid features.
  • RCE: High Risk Reduction. Directly prevents certain RCE vectors by disabling inclusion tags in Liquid configuration.
  • Information Disclosure: Medium Risk Reduction. Makes it harder for attackers to leverage Liquid features for data exfiltration in SSTI scenarios.

• Currently Implemented:

  • Limited Tag Usage (Guideline): Development team generally avoids using render, include, and layout tags unless strictly necessary, based on internal guidelines. This is not enforced by Liquid configuration.

• Missing Implementation:

  • Formal Feature Restriction Configuration: No explicit configuration in the Liquid engine itself to disable or restrict specific tags and filters. Reliance on developer guidelines is not sufficient.
  • Regular Configuration Review: No scheduled reviews of Liquid engine configuration to ensure feature restrictions are up-to-date and effective.

Mitigation Strategy: 3. Liquid Template Security Audits and Reviews

3. Liquid Template Security Audits and Reviews

• Mitigation Strategy: Liquid Template Security Audits and Reviews

• Description:

  1. Establish Liquid-Specific Review Focus: When conducting code reviews, explicitly include a focus on Liquid template security. Train developers and security reviewers on common SSTI and Liquid-specific vulnerabilities.
  2. Liquid Template Code Review Process: During Liquid template code reviews:
     • Check for User Input Handling in Templates: Specifically examine how user input is incorporated within Liquid templates. Verify proper output encoding using Liquid filters.
     • Review Logic Complexity in Templates: Assess the complexity of logic within Liquid templates. Simpler templates are easier to review and secure.
     • Look for Dangerous Liquid Tag Usage: Pay close attention to the usage of potentially dangerous Liquid tags like render, include, layout, and custom filters within the templates. Ensure they are used securely and only when absolutely necessary.
  3. Automated SSTI Vulnerability Scanning for Liquid: Utilize Static Application Security Testing (SAST) tools that can specifically analyze Liquid template syntax and detect potential SSTI vulnerabilities.
     • SAST Tool Selection (Liquid Support): Choose a SAST tool that explicitly supports Liquid template analysis or can be configured to detect SSTI patterns in Liquid syntax.
     • Configuration and Integration (Liquid Templates): Configure the SAST tool to specifically scan Liquid template files during builds or code commits.

• Threats Mitigated:

  • Server-Side Template Injection (SSTI): High Severity. Proactive audits and reviews specifically focused on Liquid templates help identify and fix SSTI vulnerabilities in Liquid code before they are exploited.
  • Logic Bugs and Business Logic Flaws in Templates: Medium Severity. Code reviews of Liquid templates can catch logic errors and business logic flaws within the template code that could lead to unexpected behavior or security issues.

• Impact:

  • SSTI: High Risk Reduction. Significantly reduces the likelihood of SSTI vulnerabilities in Liquid templates reaching production.
  • Logic Bugs and Business Logic Flaws in Templates: Medium Risk Reduction. Improves the overall quality and security of Liquid templates.

• Currently Implemented:

  • Code Reviews (General): Code reviews are conducted for all code changes, including template modifications, but security is not always the primary focus in Liquid template reviews, and Liquid-specific vulnerabilities might be missed.

• Missing Implementation:

  • Security-Focused Liquid Template Reviews: No dedicated security-focused reviews specifically for Liquid templates. General code reviews may not catch Liquid-specific vulnerabilities.
  • Automated SAST for Liquid SSTI: No SAST tool integrated into the CI/CD pipeline to automatically scan for SSTI vulnerabilities in Liquid templates.

Mitigation Strategy: 4. Minimize Data Exposure Passed to Liquid Templates

4. Minimize Data Exposure Passed to Liquid Templates

• Mitigation Strategy: Minimize Data Exposure Passed to Liquid Templates

• Description:

  1. Data Necessity Analysis for Liquid Templates: For each Liquid template, carefully analyze what data is absolutely necessary for the template to render correctly.
  2. Principle of Least Privilege for Data (in Liquid Context): Only pass the minimum required data to Liquid templates from the backend. Avoid passing entire objects or datasets if only specific attributes are needed within the template.
     • Data Filtering Before Liquid: Filter and select only the necessary data in the backend code before passing it to the Liquid engine.
     • Data Transformation Before Liquid: Transform data into a format that is suitable for the template and minimizes exposure of sensitive information before it reaches Liquid.
  3. Abstract Data Access with Liquid Helpers (Filters/Functions): Instead of directly exposing raw data structures in templates, use Liquid helper functions or filters to retrieve and format data within the template.
     • Liquid Helper Functions/Filters: Create custom Liquid filters or helper functions that encapsulate data access logic within the Liquid template environment. Templates should call these helpers to get data instead of directly accessing data objects passed from the backend.
     • Data Sanitization in Liquid Helpers: Implement data sanitization and formatting within these Liquid helper functions to ensure data is safe before being used in templates.

• Threats Mitigated:

  • Information Disclosure: High Severity. Minimizing data exposure passed to Liquid templates reduces the amount of sensitive information that could be leaked if an SSTI vulnerability is exploited or through accidental template errors within the Liquid rendering process.
  • Server-Side Template Injection (SSTI): Medium Severity. While not directly preventing SSTI, limiting data exposure to Liquid reduces the potential impact of a successful SSTI attack by limiting the attacker's access to sensitive data through the Liquid template context.

• Impact:

  • Information Disclosure: High Risk Reduction. Significantly reduces the potential for data leakage through Liquid templates.
  • SSTI: Medium Risk Reduction. Limits the damage that can be done if SSTI occurs within the Liquid context.

• Currently Implemented:

  • Data Filtering (Basic): Backend code generally filters data to some extent before passing it to templates, but not always with a strict principle of least privilege specifically for Liquid templates.

• Missing Implementation:

  • Strict Data Necessity Analysis for Liquid: No formal process for analyzing data necessity specifically for each Liquid template. Data exposure minimization to Liquid is not consistently applied.
  • Helper Functions/Filters for Liquid Data Access: Limited use of custom Liquid helper functions or filters to abstract data access within templates. Templates often directly access data objects passed from the backend.
  • Data Sanitization in Liquid Helpers: Data sanitization is not consistently implemented within custom Liquid helper functions.

Mitigation Strategy: 5. Secure Error Handling within Liquid Templates

5. Secure Error Handling within Liquid Templates

• Mitigation Strategy: Secure Error Handling within Liquid Templates

• Description:

  1. Implement Error Handling in Liquid Templates: Use Liquid's error handling mechanisms (if available in the specific Liquid implementation) or implement custom error handling logic directly within Liquid templates to gracefully handle potential errors during rendering.
     • rescue blocks (if supported by Liquid): Utilize rescue blocks or similar constructs within Liquid templates to catch errors during template execution.
     • Conditional Checks in Liquid: Use conditional statements (if, else) within Liquid templates to check for data existence or validity before attempting to access or render it, preventing errors due to missing or invalid data.
  2. Prevent Sensitive Information in Liquid Error Output: Ensure that if Liquid error messages are ever displayed (even in development), they do not contain sensitive information. Configure Liquid to produce generic error messages or handle errors silently in production.

• Threats Mitigated:

  • Information Disclosure: Medium Severity. Prevents accidental disclosure of sensitive information through detailed error messages potentially generated by Liquid during template rendering.

• Impact:

  • Information Disclosure: Medium Risk Reduction. Reduces the risk of leaking sensitive information in Liquid-related error messages.

• Currently Implemented:

  • Generic Error Pages (General Application): Generic error pages are displayed to users for unhandled exceptions, but specific error handling within Liquid templates is limited.

• Missing Implementation:

  • Template-Level Error Handling in Liquid: Lack of robust error handling logic within Liquid templates themselves. Reliance on generic application-level error handling.
  • Liquid Error Message Sanitization: No specific configuration or process to ensure Liquid error messages are sanitized to prevent accidental disclosure of sensitive data, even in non-production environments.

Mitigation Strategy: 6. Limit Liquid Template Complexity

6. Limit Liquid Template Complexity

• Mitigation Strategy: Limit Liquid Template Complexity

• Description:

  1. Establish Liquid Template Complexity Metrics: Define metrics to measure the complexity of Liquid templates, such as:
     • Template File Size: Limit the maximum size of Liquid template files.
     • Number of Lines of Liquid Code: Limit the number of lines of Liquid code in a template.
     • Nesting Depth of Liquid Tags: Limit the depth of nested Liquid tags and control structures.
     • Number of Liquid Includes/Renders: Limit the number of include or render tags within a single Liquid template.
  2. Implement Liquid Template Complexity Checks: Implement automated checks to enforce template complexity limits specifically for Liquid templates.
     • Linting Tools for Liquid: Extend or create linting tools to analyze Liquid templates and enforce complexity metrics.
     • Build-Time Checks for Liquid: Integrate complexity checks into the build process to fail builds if Liquid templates exceed defined limits.
  3. Restrict Liquid Loop Iterations and Recursion (If Applicable): If the Liquid implementation allows loops or recursive includes, configure or implement limits specifically within the Liquid environment to prevent excessive resource consumption during template rendering.
     • Loop Iteration Limits in Liquid: Configure Liquid engine or implement custom logic to limit the maximum number of iterations in for loops within Liquid templates.
     • Recursion Depth Limits in Liquid: If recursive includes are used in Liquid, set a maximum recursion depth within the Liquid engine or custom logic to prevent infinite recursion.

• Threats Mitigated:

  • Denial of Service (DoS): Medium Severity. Limiting Liquid template complexity prevents excessively resource-intensive templates that could lead to DoS during Liquid template rendering.

• Impact:

  • DoS: Medium Risk Reduction. Reduces the risk of DoS attacks caused by overly complex Liquid templates.

• Currently Implemented:

  • Informal Complexity Guidelines: Development team generally aims for simple Liquid templates, but no formal complexity limits or automated checks specifically for Liquid templates are in place.

• Missing Implementation:

  • Formal Liquid Complexity Metrics: No defined metrics for Liquid template complexity.
  • Automated Liquid Complexity Checks: No automated tools or build-time checks to enforce Liquid template complexity limits.
  • Loop/Recursion Limits in Liquid: No explicit limits on loop iterations or recursion depth within the Liquid engine or custom logic.

Mitigation Strategy: 7. Monitor Liquid Template Rendering Performance

7. Monitor Liquid Template Rendering Performance

• Mitigation Strategy: Monitor Liquid Template Rendering Performance

• Description:

  1. Monitor Liquid Rendering Time: Implement monitoring to specifically track the rendering time of Liquid templates in production.
     • Liquid Rendering Time Metrics: Collect metrics on the time taken to render each Liquid template or template type.
     • Performance Dashboards for Liquid: Create dashboards to visualize Liquid template rendering performance and identify performance bottlenecks or anomalies related to Liquid template processing.
  2. Establish Liquid Performance Baselines and Alerts: Establish baseline performance metrics for Liquid template rendering and set up alerts for deviations from these baselines.
     • Thresholds for Liquid Rendering Alerts: Define thresholds for Liquid rendering time that trigger alerts when exceeded.
     • Automated Alerting System for Liquid: Integrate performance monitoring with an alerting system to notify operations teams of performance issues specifically related to Liquid template rendering.

• Threats Mitigated:

  • Denial of Service (DoS): Medium Severity. Monitoring Liquid template rendering performance helps identify and address performance issues that could contribute to DoS vulnerabilities related to Liquid template processing.
  • Performance Degradation: Medium Severity. Monitoring specifically for Liquid template rendering helps identify and address performance issues within the template rendering layer, preventing overall application performance degradation.

• Impact:

  • DoS: Medium Risk Reduction. Reduces the risk of DoS attacks related to slow Liquid template rendering by enabling proactive performance management.
  • Performance Degradation: High Risk Reduction. Proactive monitoring and alerting of Liquid template rendering performance help maintain application performance.

• Currently Implemented:

  • General Application Performance Monitoring: General application performance monitoring is in place, but may not specifically track Liquid template rendering performance in detail.

• Missing Implementation:

  • Liquid Rendering Specific Monitoring: No dedicated monitoring specifically for Liquid template rendering performance metrics.
  • Performance Baselines and Alerts for Liquid Templates: No established performance baselines or alerts specifically for Liquid template rendering.