Node Nunjucks Server Side Template Injection (SSTI) Scanner

Nunjucks is a versatile template engine designed for web application development using Node.js platforms like Express or Connect. It is often utilized for rendering dynamic content on web pages, supporting a syntax similar to Jinja2. Developers use Nunjucks for its flexibility, ease of integration, and ability to enhance the user experience in complex web applications. As organizations increasingly depend on Node.js-based web frameworks, Nunjucks continues to be a popular choice for building robust applications. However, with its extensive features, it's crucial to manage security risks associated with its deployment effectively. Being aware of potential vulnerabilities is essential for maintaining secure Node.js applications.

Server Side Template Injection (SSTI) is a vulnerability that occurs when an attacker is able to inject malicious payloads into a web application's template, which could result in arbitrary code execution. This type of vulnerability is often found in web applications that use template engines to render page content. When exploited, SSTI allows attackers to execute code on the server, leading to unauthorized access and potential data breaches. User input that is not properly sanitized can introduce SSTI vulnerabilities, making it critical for developers to enforce strict input validation. The impact of SSTI can vary from minor information leaks to taking complete control of the server.

The vulnerability within Node Nunjucks can be technically exploited by injecting unsanitized user input directly into template structures, causing unexpected behavior in rendering web pages. Critical endpoints such as `/page?name=` could be targeted by attackers using SSTI payloads to exploit vulnerabilities. Parameters passed into templates without sufficient validation become susceptible to injection. An exploitation vector involves using execution functions like `execSync()` in Node.js through the SSTI payload. The vulnerability is identified by patterns indicating successful injection, such as accessing sensitive files or executing commands. Attacks using SSTI can remain stealthy if the application logs or debug messages are not carefully monitored.

When SSTI vulnerabilities in Node Nunjucks are exploited, attackers can perform arbitrary code execution on the server. This could lead to data compromise, unauthorized administrative access, or even service disruption. Sensitive information, such as environment variables and system files, can be accessed, potentially leading to further security breaches. An exploited SSTI vulnerability provides a foothold for lateral movement within the network, increasing the risk of extensive damage. Correctly identifying and mitigating SSTI is crucial for preventing unauthorized access and ensuring the security of web applications built with Node.js.