CVE-2023-30581 is a critical vulnerability that allows bad actors to bypass the experimental policy mechanism of Node.js by taking advantage of the __proto__ feature. If exploited, this vulnerability can enable attackers to require modules outside of the policy.json definition, potentially leading to various security breaches.

This blog post provides an in-depth look at the exploit, demonstrates a code snippet that showcases the issue, and provides links to original references. We will also briefly touch upon the affected Node.js release lines: v16, v18, and v20.

Important note: At the time this CVE was issued, the policy mechanism was still an experimental feature of Node.js.

What is CVE-2023-30581?

CVE-2023-30581 is a security vulnerability that targets a weakness in the experimental policy mechanism implemented in Node.js. By utilizing the __proto__ feature in process.mainModule.__proto__.require(), threat actors can easily bypass the policy limitations and require modules outside of the policy.json definition.

For those unfamiliar with __proto__, it is a property that enables direct access to an object's internal prototype. This is different from the standard prototype property, which provides access to an object constructor's prototype. The inherent risks associated with __proto__ have been widely documented, primarily because it allows the modification of an object's prototype chain and can, therefore, cause unintentional side effects.

Exploit Details & Code Sample

Below is a code snippet that demonstrates the vulnerability present in the affected versions of Node.js:

// sample.js
const policyBypass = process.mainModule.__proto__.require;

// requiring a restricted module
const fs = policyBypass("fs");

// using the restricted module, for example, reading a sensitive file
fs.readFile("/etc/passwd", "utf-8", (err, data) => {
  if (err) {
    console.error(err);
    return;
  }

  console.log("Policy Bypassed! Sensitive data:", data);
});

In the above code snippet, the policyBypass variable utilizes the __proto__ feature to bypass policy restrictions and gain access to restricted Node.js modules. This enables threat actors to require any module, even when it is explicitly disabled by the policy.json.

Affected Node.js Versions

This vulnerability affects all Node.js users who are using the experimental policy mechanism in the following active release lines:

v20.x

You are urged to review your Node.js deployments and take appropriate precautions to secure your applications.

- CVE-2023-30581 Record in Mitre Database: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-30581
- Node.js Security Bulletin: https://nodejs.org/en/blog/security/vulnerability-alert/
- Node.js Experimental Policy Mechanism Documentation: https://nodejs.org/api/policy.html

Conclusion

CVE-2023-30581 is a significant security vulnerability present in the experimental policy mechanism of Node.js. It allows attackers to bypass policy.json restrictions, which may lead to severe security risks. Any user operating an application using the affected Node.js versions (v16, v18, or v20) should take immediate steps to review their deployments and secure their environment.

As always, it is essential to keep your software updated, applying security patches promptly, and following best practices to safeguard your application against potential threats.

Timeline

Published on: 11/23/2023 00:15:07 UTC
Last modified on: 11/30/2023 01:52:32 UTC