Identification of Server-Side Template Injection

Server-Side Template Injection (SSTI) is a type of vulnerability that occurs when an attacker is able to inject malicious code into a server-side template engine. This allows them to execute arbitrary code within the server's context, potentially leading to data leakage, remote code execution, or other security breaches. Identifying SSTI vulnerabilities involves examining how templates are processed and rendered on the server side. Here's how you can identify Server-Side Template Injection vulnerabilities:


  1. Reviewing Template Engines in Use: Identify the template engines used in the application's server-side code. Common template engines include Jinja2, Freemarker, Thymeleaf, and others.
  2. Identifying User-Controlled Input: Look for places in the application where user-controlled input is used directly within templates. This can include parameters passed to template rendering functions or variables interpolated into templates.
  3. Testing for Template Injection: Inject template-specific payloads into user-controllable inputs to see if they are evaluated as code. For example, try injecting expressions such as ${7*7} or ${7*'7'} and observe the application's response.
  4. Analyzing Error Messages: Pay attention to error messages or stack traces returned by the server. Look for any indications of template parsing errors, unexpected output, or exceptions related to template rendering.
  5. Reviewing Template Context: Understand the context in which templates are rendered and the variables and functions available within the template context. Determine if there are any unsafe functions or variables that could be abused for code execution.
  6. Checking Template Includes: Examine how templates include or import other templates or files. Insecure includes or imports can lead to SSTI vulnerabilities if user-controlled input is used to specify the template path.


  • Example 1: During testing, a penetration tester discovers that the application uses a template engine that is vulnerable to SSTI. By injecting a payload such as ${7*7}, the tester is able to execute arbitrary code within the template context, leading to potential data leakage or remote code execution.
  • Example 2: The tester finds that the application includes user-controlled input in a template filename without proper validation. This allows an attacker to manipulate the filename and inject malicious templates, leading to SSTI vulnerabilities.


  1. Input Validation and Sanitization: Validate and sanitize user-controlled input before using it in templates to prevent injection attacks.
  2. Contextual Autoescaping: Use template engines that support contextual autoescaping to automatically escape user input based on its context within the template.
  3. Whitelisting Variables: Whitelist safe variables and functions that can be used within templates and avoid exposing sensitive server-side objects or functions.
  4. Template Sandbox: Consider running template rendering processes in a sandboxed environment with restricted access to server resources and functionality.
  5. Regular Security Audits: Conduct regular security audits and code reviews to identify and address SSTI vulnerabilities in server-side code.
  6. Security Training: Educate developers about the risks of SSTI vulnerabilities and best practices for secure template rendering.

By identifying and mitigating Server-Side Template Injection vulnerabilities, organizations can prevent unauthorized code execution and protect the integrity of their server-side applications.