CVE-2023-47833 - Exploiting XSS in Jeroen Schmit Theater for WordPress (Plugin <= .18.3)

CVE-2023-47833 marks a critical security vulnerability in the popular WordPress plugin "Theater," developed by Jeroen Schmit. This plugin, often used by theaters, playhouses, and event organizers, helps in managing and displaying events on WordPress sites. But if you’re running version .18.3 or lower, your site might be wide open to Cross-site Scripting (XSS) attacks.

In this exclusive deep-dive, we’ll break down what went wrong, how the exploit works, provide code snippets, and guide you toward more secure systems. Let’s get started.

What is CVE-2023-47833?

Title: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in Jeroen Schmit Theater for WordPress Plugin <= .18.3

Vulnerability Type: XSS (Cross-Site Scripting)
CVSS Score: 6.5 (Medium)
Disclosure Date: November 2023
Original References:
- NVD: CVE-2023-47833
- WPScan Advisory

How Did the Flaw Happen?

The core issue: the Theater plugin failed to properly sanitize and neutralize user input before embedding it in web pages. In practical terms, it accepted data (like event titles, locations, or organizers) from back-end forms or user-generated fields and then rendered that data in the site's HTML—sometimes without enough checks.

So, if an attacker managed to sneak some malicious JavaScript into one of those fields, every visitor or site admin who eventually saw that event listing would unknowingly run dangerous code.

Take this (simplified) PHP code snippet as an illustration, showing how an unsafe render might look

// In the vulnerable plugin:
echo '<h3>' . $_POST['event_title'] . '</h3>';

If an attacker submits

<script>alert('Hacked!');</script>

as the event title, the site outputs

<h3><script>alert('Hacked!');</script></h3>

Anyone viewing the events gets a popup. But real attackers could steal cookies, redirect users, or deface the page.

Proper sanitization should look like

echo '<h3>' . esc_html($_POST['event_title']) . '</h3>';

This disables <script> and other dangerous HTML tags.

Attack scenario

1. Attacker gains access to submit or edit events (could be from a compromised account, low-privilege user, or open event submission form).

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Remediation

If you use Theater for WordPress:
- Update immediately to the latest fixed version (check official plugin page).

Review event data, looking for suspicious scripts or unfamiliar events.

For developers:
- Always use output neutralization like esc_html(), esc_attr(), or similar WordPress escaping functions.

Conclusion

CVE-2023-47833 is a serious XSS vulnerability waving a red flag for thousands of WordPress event websites. If you’re affected, time is of the essence—patch it now and review your event listings!

Further Reading:
- WordPress XSS Guide
- Official CVE Entry
- WPScan Details

Timeline

Published on: 11/23/2023 00:15:08 UTC
Last modified on: 11/28/2023 20:25:42 UTC