Identification of Template Injection

Template injection occurs when user input is improperly sanitized and integrated into templates, leading to remote code execution or other malicious outcomes. This vulnerability typically exists in web applications that use templating engines to dynamically generate HTML or other output. Identifying template injection vulnerabilities requires understanding the templating engines used by the application and recognizing the points where user input could influence the template output. Here's how a penetration tester might identify and assess template injection vulnerabilities:


  1. User Input Handling: Check how user input is integrated into templates. If input is directly embedded without proper sanitization or escaping, it might lead to template injection.
  2. Template Engine Evaluation: Understand the template engine being used (e.g., Jinja2, FreeMarker, Twig) and its potential vulnerabilities. Some engines allow for dynamic evaluation of expressions, which could be exploited.
  3. Error Messages and Output: Inputting unexpected values or template expressions can lead to error messages or anomalies in the output, indicating a potential injection point.
  4. Dynamic Content Generation: Identify areas where the application generates content dynamically based on user input. These are potential injection points.
  5. Code Review: During a code review, look for instances where user-controlled data is concatenated with template code or where templates are dynamically constructed from user input.


  • Example 1: A penetration tester discovers that a web application using the Jinja2 templating engine displays user input directly in an error message. By injecting specific Jinja2 syntax, the tester is able to execute arbitrary code on the server.
  • Example 2: In a different scenario, an application uses user input to form a part of a SQL query within a template. The tester injects template directives to modify the query, leading to a successful SQL injection.

Exploitation and Impact

  • Remote Code Execution (RCE): If the attacker can inject template directives, they might execute arbitrary code, depending on the template engine's capabilities.
  • Information Disclosure: An attacker could leverage template injection to disclose sensitive information from the application or server.
  • Cross-Site Scripting (XSS): If the template injection occurs in a context that's rendered in users' browsers, it could lead to XSS vulnerabilities.


  1. Input Sanitization: Always sanitize user input before including it in templates. Ensure that the input is treated as plain text and not as executable code.
  2. Use Safe APIs: Utilize APIs provided by the templating engine that automatically escape input to prevent injection.
  3. Minimal Privileges: Ensure that the template engine runs with minimal privileges, limiting the potential impact of a successful injection.
  4. Template Validation: Implement strict validation for template syntax, rejecting templates that contain unexpected or dangerous constructs.
  5. Security Testing: Regularly test applications for template injection vulnerabilities, particularly in places where user input interacts with template systems.

By methodically testing and reviewing areas where user input interacts with templating engines, penetration testers can identify and help remediate template injection vulnerabilities, thereby preventing potential exploitation and safeguarding the application.