In this article, we will dive deep into an important vulnerability found in the ejs (Embedded JavaScript templates) package versions prior to 3.1.10 for Node.js. We will discuss the details of this security flaw, its potential impact on applications, how it can be exploited, and the necessary steps to mitigate the risks associated with it. Please note that this article is for informative purposes only and should not be considered as a tutorial for exploiting the discussed vulnerability.

CVE-2024-33883 Overview

The vulnerability in question is identified as CVE-2024-33883. It stems from the fact that the ejs package, which stands for Embedded JavaScript templates, lack specific pollution protection. This security issue affects versions of the package released before 3.1.10.

The ejs package is widely used in the Node.js ecosystem to provide features like template rendering, custom delimiters, script blocking, support for dynamic includes, and other functionalities that bridge the gap between code execution and markup presentation.

Regarding pollution protection, it is essential to understand that the lack of this security feature allows attackers to perform a "prototype pollution" exploit. Prototype pollution is a vulnerability that occurs when an attacker manipulates the prototype of a JavaScript object and alters its properties, causing an application to behave unexpectedly.

The ejs vulnerability can lead to several security risks, including denial of service attacks, unauthorized access, remote code execution, and even data leakage if left unpatched.

Exploit Details

To demonstrate the vulnerability, let's consider a simple Express application that uses the ejs package to render the templates. Note that the example assumes you're using the vulnerable ejs package version - in this case, version 3.1.9 or earlier.

Suppose we have an index.ejs code snippet embedded in an Express application

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1." />
    <title>Sample EJS Page</title>
  </head>
  <body>
    <% include header %>

    <h1>Welcome to my website!</h1>
    <% include footer %>
  </body>
</html>

This code snippet is rendered to the user when they visit the home page of the application. Now, suppose an attacker sends a specially crafted HTTP request that takes advantage of the prototype pollution vulnerability:

GET /?__proto__=__defineGetter__ HTTP/1.1
Host: example.com
User-Agent: Mozilla/5. (X11; Ubuntu; Linux x86_64; rv:88.) Gecko/20100101 Firefox/88.
Accept: text/html,application/xhtml+xml,application/xml;q=.9,image/webp,*/*;q=.8
Accept-Language: en-US,en;q=.5
Accept-Encoding: gzip, deflate
Connection: close
Upgrade-Insecure-Requests: 1
Cache-Control: max-age=

This request contains a malicious payload that exploits the ain question, leading to prototype pollution by making the include function execute arbitrary JavaScript code even if it is blocked by the default security configuration of the ejs package.

The best way to protect against this vulnerability is to upgrade the ejs package to version 3.1.10 or newer, which includes proper prototype pollution protection.

1. CVE Details
2. National Vulnerability Database
3. GitHub Security Advisory

To mitigate the vulnerability, ensure to update your ejs package to version 3.1.10 or newer using the command:

npm install ejs@latest

This update will include proper pollution protection, and your application will be significantly less susceptible to potential exploitation.

Conclusion

In this article, we examined CVE-2024-33883, a significant vulnerability in the ejs package for Node.js. The flaw originates from missing pollution protection, allowing attackers to exploit prototype pollution and cause severe security issues. It is crucial to update your ejs package to version 3.1.10 or later to ensure the security of your applications. Stay safe and keep your dependencies up to date!

Timeline

Published on: 04/28/2024 16:15:23 UTC
Last modified on: 08/02/2024 02:42:59 UTC