Understanding Server-Side Template Injection (SSTI) Risks, Exploitation, and Prevention

Server-Side Template Injection (SSTI) is a critical vulnerability that can compromise the security of web applications. It occurs when user input is embedded within templates processed by server-side templating engines without proper validation or sanitization. In this article, we’ll explore what SSTI is, how it can be exploited, the risks associated with it, and the strategies to prevent it.

What is Server-Side Template Injection (SSTI)?

Server-Side Template Injection (SSTI) is a vulnerability that arises when user-controlled data is injected into templates processed by server-side templating engines. These engines are responsible for generating dynamic content in web applications, and when they improperly handle user input, it can lead to remote code execution (RCE) and other severe security issues.

How is SSTI Exploited?

SSTI can be exploited by injecting specially crafted payloads into input fields that are later processed by server-side templating engines. Attackers typically manipulate template syntax to execute arbitrary code, access sensitive data, or perform other malicious actions. For example, in a Flask web application using the Jinja2 templating engine, an attacker might inject the following payload