CVE-2023-23313 - Critical XSS Vulnerability in DrayTek Routers

If you’re managing a network using DrayTek routers, it’s time to pay close attention. CVE-2023-23313 is a new security vulnerability affecting a wide range of DrayTek devices due to improper input handling in the web management interface. Attackers can exploit this bug to inject malicious code, running it inside your browser when accessing the device's administrative portal. This post explains how this works, which models are at risk, and shows actual code examples, so you can check and protect your device right now.

What is CVE-2023-23313?

CVE-2023-23313 is a Cross Site Scripting (XSS) vulnerability in the wlogin.cgi and user_login.cgi scripts on DrayTek routers. When you log into your router's web admin interface, these scripts do not sanitize input correctly. As a result, an attacker can send crafted input or trick an admin into clicking a malicious link, injecting code that runs in your browser with your credentials and permissions.

For a full list and confirmation, always check the official DrayTek advisory and CVE record

- DrayTek Security Advisories
- NIST NVD: CVE-2023-23313

How Does The Exploit Work?

When an administrator tries to log in, these CGI scripts process the login request. However, instead of removing dangerous code, they allow certain input directly into the web page.

Suppose the attacker crafts a special link containing malicious JavaScript and sends it to the target (phishing, email, etc.). When the admin clicks the link and tries to log in, the malicious code executes.

Real-World Example

The login CGI scripts take parameters like username and error_msg and reflect them on the HTML page. This means an attacker can inject their own script like so:

Exploit URL Structure

http://router_ip/wlogin.cgi?username=<script>alert('XSS')</script>;

Or, using user_login.cgi

http://router_ip/user_login.cgi?username=<img src="x" onerror="alert('XSS')">

The script takes the username parameter and displays it in an HTML form.

- If the input isn’t sanitized, the browser reads the injected JavaScript as a command, not a string.
- The attacker's code (here an alert(), but could be anything malicious) runs with the admin's privileges.

Sample Vulnerable Page Output

<form action="/user_login.cgi">
  Username: <script>alert('XSS')</script>
  Password: <input type="password" name="password">
  <input type="submit" value="Login">
</form>

For proof of concept, all the attacker has to do is get the admin to click or visit a crafted URL.

Hijack sessions or redirect traffic

Anyone with access to the login portal (even only to the LAN) can potentially exploit this if they trick the admin.

Check your router’s firmware version. Are you running a version listed above?

2. Update firmware right away. DrayTek has already provided patches for most affected models. Download the latest from DrayTek’s support site.
3. Restrict management interface access. Only allow trusted devices or networks to connect to the admin web interface.
4. Educate your admins. Don’t click unknown links; always type your router’s IP or hostname directly.

More Technical Resources

- Original DrayTek Advisory (Jan 2023)
- CVE-2023-23313 NVD Listing
- Exploit Proof of Concept by VulnCheck

Conclusion

CVE-2023-23313 is a serious security flaw in popular DrayTek routers, making it critical for anyone relying on these devices to update as soon as possible. XSS can lead to total compromise of your device and possibly your network. Patching prevents these attacks, but you should still reduce exposure and train your team to recognize phishing links.

If in doubt, always check the latest updates from DrayTek and consider subscribing to their security notifications.

Stay protected, and patch your routers today!

*This was an exclusive overview tailored for network admins and security-conscious users. If you found this post helpful, share it with your IT team or anyone managing DrayTek hardware.*

Timeline

Published on: 03/03/2023 22:15:00 UTC
Last modified on: 03/10/2023 14:52:00 UTC