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Server-Side Template Injection (SSTI)

Web Application SecurityTemplate EnginesVulnerability DetectionExploitation TechniquesSecure Coding Practices

Server-Side Template Injection (SSTI) is a critical security vulnerability that occurs when user input is improperly handled and injected into a template engine, allowing attackers to execute arbitrary code on the server. This vulnerability can lead to unauthorized code execution, compromising the security of web applications.

Key Points

  • SSTI occurs when user input is treated as part of the template code.
  • Common template engines like Smarty (PHP), Pug (NodeJS), and Jinja2 (Python) can be exploited if user inputs are not properly sanitized.
  • Detection involves injecting specific payloads to see if they are executed by the template engine.

Detailed Explanation

What is SSTI?

SSTI is a security flaw where user input is not properly sanitized and is interpreted as part of the template code. This allows attackers to inject malicious code into the template engine, leading to unauthorized code execution on the server.

Common Template Engines

Template EngineLanguage
SmartyPHP
PugNodeJS
Jinja2Python

Detection Methods

Detection of SSTI involves injecting specific payloads to see if they are executed by the template engine. For example, in a web application using Jinja2, an attacker might input {{7*7}}. If the output is 49, it confirms the presence of SSTI.

Practical Example

In a web application using Jinja2, an attacker might input {{7*7}}. If the output is 49, it confirms the presence of SSTI.

Real-World Application

An e-commerce site that dynamically generates product pages using user-supplied data could be vulnerable to SSTI if it doesn't properly sanitize inputs. This allows attackers to manipulate server-side code, compromising the security of the application.

Key Takeaways

  • Always sanitize and validate user inputs to prevent SSTI.
  • Regularly test web applications for SSTI vulnerabilities using tools like SSTImap.
  • Understand the specific syntax and functions of the template engine in use to better protect against SSTI.

Learn More

For more information on SSTI and how to protect against it, consider exploring the following resources: