In fall 2023, CVE-2023-43339 revealed a dangerous flaw in _CMS Made Simple_ (CMSMS) version 2.2.18. This vulnerability allows a local attacker to run harmful scripts just by entering tricky values into database config fields. In this post, we’ll break down what’s happening, walk through a practical exploit example, and show how to fix or avoid the issue.

What Is CMS Made Simple?

CMS Made Simple is a popular, open-source content management system. It’s often used by small to midsize websites for easy content updates and design management. The system uses a web-based installer for setting up the database, which is where our problem originates.

Entry Points: Database Name, Database User, Database Port fields during installation

The CMS installer does not sanitize or escape values entered in these fields. Any JavaScript inserted here can end up in the HTML on follow-up screens or in error logs, which then executes in the browser.

1. Launch the Installer

Any attacker who gets local access to the web root (think a customer, support staff, or someone who gets limited FTP access) can start a new install or even trick a site admin to re-run the installer.

2. Enter a Malicious Payload

Instead of a normal database value, the attacker enters JavaScript. For example, in the “Database Name” field:

"><script>alert('XSS in CMSMS!')</script>

3. Complete or Break the Install

The installer will move to the next step—or give an error if the database info is invalid. But that doesn’t matter: the attacker’s payload ends up reflected in the source code of the install/upgrade/error pages.

4. Trigger XSS Execution

When anyone (admin, another user) loads that config or views installer output, the browser runs the injected script.

Inside install/index.php, code might look like

// Simplified for illustration
echo "<input name='db_name' value='" . $_SESSION['db_name'] . "' />";

No escaping means the code above outputs

<input name='db_name' value='"><script>alert("XSS in CMSMS!")</script>' />

A real test payload, safe for demonstration, is

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

Enter it as the Database User in the install screen.

What happens next:
When the installer loads the review or error step, your browser shows a popup “XSS in CMSMS.” This means JavaScript of any kind will launch—including something more dangerous in a real attack.

How to Fix CVE-2023-43339

CMSMS needs to sanitize input and escape output everywhere user data is shown. Until an official patch, take these steps:

Change lines like

echo "<input name='db_name' value='" . $_SESSION['db_name'] . "' />";

to:

echo "<input name='db_name' value='" . htmlspecialchars($_SESSION['db_name'], ENT_QUOTES, 'UTF-8') . "' />";

After install, remove the install directory or deny access through .htaccess

<Directory /path/to/cmsms/install>
    Order allow,deny
    Deny from all
</Directory>

3. Patch or Upgrade ASAP

Monitor the official CMSMS bug tracker or GitHub repo for fixes.

4. Watch for Unusual Users

If you see odd database configs or unexpected users, investigate immediately.

References and More Reading

- NVD CVE-2023-43339 Entry
- Exploit Details on Exploit-DB
- CMSMS Security Announcements
- Cross-Site Scripting (XSS), OWASP

Closing Thoughts

CVE-2023-43339 is proof that even safe-looking installer forms can pose serious risks if user input isn’t handled correctly. If you run CMS Made Simple, remove or secure your installer immediately and monitor for security updates. Don’t let a simple local XSS flaw lead to a full-scale breach!

*Stay safe, patch early, and always sanitize your input.*


Have questions, comments, or found this in the wild? Drop a note below or report responsibly.

Timeline

Published on: 09/25/2023 16:15:14 UTC
Last modified on: 11/08/2023 03:14:03 UTC