CVE-2023-40874 - How a Simple Bug in DedeCMS Allowed Hackers to Inject Malicious Scripts (With Code Example)

In the world of content management systems (CMS), security should always be a primary concern. Recently, a high-impact vulnerability was discovered in DedeCMS—a popular open-source CMS in China. Tracked as CVE-2023-40874, this vulnerability allows attackers to inject malicious scripts using simple form inputs. In this post, I’ll explain how the vulnerability works, show you how attackers can exploit it, and give advice on what to do if you’re using a vulnerable version.

What is DedeCMS?

DedeCMS powers thousands of websites, especially in Chinese-speaking regions. Easy templating and extensibility make it an attractive choice. Sadly, these benefits also come with risk: old code, limited maintenance, and, sometimes, dangerous bugs.

Summary of CVE-2023-40874

The flaw affects DedeCMS versions up to and including 5.7.110. The issue is found in the vote_add.php page, where certain user-provided parameters are not properly sanitized. An attacker can inject JavaScript into the votename and voteitem1 fields, resulting in cross-site scripting (XSS).

Official References

- Mitre NVD entry for CVE-2023-40874
- DedeCMS Official Website

How Does the Vulnerability Work?

The root cause here is lack of input validation. The vote_add.php script simply takes data from a web form and uses it directly, without stripping potentially dangerous content.

voteitem1

Everything entered into these fields gets stored and later shown to other users, without any cleaning.

Imagine you’re filling out a poll as follows

- Poll Name (votename): <script>alert('XSS!')</script>

First Option (voteitem1): <img src=x onerror=alert('Hacked by XSS!')>

When a site administrator or user later reviews this poll’s summary, their browser will execute the JavaScript, leading to a popup alert (or worse, theft of cookies or credentials).

Here’s a stripped-down example of the code (vulnerable part)

// vote_add.php (Simplified Example)
$votename = $_POST['votename'];
$voteitem1 = $_POST['voteitem1'];

// Store into database (naively)
$query = "INSERT INTO votes (name, item1) VALUES ('$votename', '$voteitem1')";
mysql_query($query);

// Later, displaying the poll
echo "Poll name: $votename";
echo "First option: $voteitem1";

Problem: No htmlspecialchars() or filtering is applied. Thus, whatever is submitted gets output as-is.

You can test this easily on a DedeCMS site (for educational purposes only!)

1. Visit /dede/vote_add.php
2. In "Poll Name", input: <script>alert('Vulnerable!')</script>

Submit the form.

5. Go to the poll list or detail page. You’ll see the alert pop up—evidence that your code was executed.

Screenshot (For Illustration)

Poll name: <script>alert('Vulnerable!')</script>
First option: <img src=x onerror=alert(document.cookie)>

Spread malware

All with just a few characters entered in a normal form!

How To Fix or Mitigate

If you are running DedeCMS 5.7.110 or older:
Upgrade to the latest version immediately, as this bug is critical.

Alternatively, patch your code

// Hardened version
$votename = htmlspecialchars($_POST['votename'], ENT_QUOTES, 'UTF-8');
$voteitem1 = htmlspecialchars($_POST['voteitem1'], ENT_QUOTES, 'UTF-8');

This ensures that any HTML tags are rendered harmless.

Conclusion

CVE-2023-40874 is a textbook case of why input validation matters. If you’re running an old DedeCMS, make sure to patch or upgrade ASAP. Never trust user input—ever!

For more details, always check the official CVE entry and follow the DedeCMS official website for updates.

*Disclaimer: This post is for educational and awareness purposes only. Never use security vulnerabilities for malicious activities.*

Timeline

Published on: 08/24/2023 15:15:07 UTC
Last modified on: 08/25/2023 13:19:53 UTC