In early 2024, Microsoft disclosed a critical security vulnerability (CVE-2024-20677) involving FBX files and their handling within Office products and the Windows 3D Viewer application. This vulnerability could allow attackers to execute remote code on your computer—potentially taking control of your system—simply by having you open a malicious FBX file in Word, Excel, PowerPoint, Outlook, or 3D Viewer.

In this post, we’ll break down what the issue is, how attackers might exploit it, what Microsoft is doing to protect you, and what steps you need to take. We’ll keep this accessible—no jargon, no confusion.

What is the FBX File Format?

FBX (Filmbox) is a popular 3D model format developed by Autodesk, used widely in animation, gaming, and VR/AR applications. Microsoft Office lets you embed 3D models in your documents—including FBX files—so you can create more engaging visuals in reports, slideshows, and emails.

What is CVE-2024-20677?

CVE-2024-20677 is the designation for a vulnerability in Microsoft’s handling of FBX files. The core of the problem is how Office and 3D Viewer software process, load, and render these files.

Put simply:
A specially-crafted (malicious) FBX file can trick Office or 3D Viewer into executing harmful code on your computer. An attacker could, for example, send you a Word document with an embedded 3D FBX object. Opening that document could let the attacker install malware, steal your data, or control your system remotely.

Impacted Products

- Microsoft Word, Excel, PowerPoint, Outlook (Windows/Mac)

3D Viewer for Windows

If you were using any of these, you were at risk—until the recent update.

How Could Attackers Exploit This?

The main way to exploit this vulnerability is by crafting a malicious FBX file and inserting it into an Office document or sending it directly, knowing that the victim would open it. Here’s a high-level idea of how such an attack might unfold:

Victim opens the document in Office or 3D Viewer.

5. Malicious code in the FBX file executes, potentially installing malware or taking further control.

Imagine this simplified exploit flow in pseudo-code

fbx_file = create_fbx_with_payload(shellcode)
office_document = embed_3d_model(fbx_file, into='word')
send_to_victim(office_document)
# When victim opens document
on_document_open:
    parse_fbx(fbx_file)
    execute_payload()  # this is the bad part

A real-life attack would require technical know-how to craft the FBX in a way that exploits the parser vulnerability.

Immediate Action

Starting with the January 9, 2024 security update, Microsoft disabled the ability to insert FBX files in Office and 3D Viewer:

As of February 13, 2024, the same restriction applies to 3D Viewer.

This is a *permanent* change. Even if you were using Office 2019, 2021, LTSC, or Microsoft 365, the "insert FBX" option is gone after you update.

What Happens to Old Documents?

- Already-existing 3D models inserted from FBX files will keep working—unless you used “Link to File” when inserting.

Proof-of-Concept Exploit (For Educational Purposes Only)

> WARNING: Creating malicious files is illegal unless done in a legal, ethical, and controlled environment (for research/testing with permission).
> What follows is a *simple illustration* for security education.

Here is a highly simplified Python snippet emulating how an attacker might place an exploit into an FBX file:

# Pseudo-code / illustrative -- NOT actually infectious or functional
with open('malicious.fbx', 'wb') as f:
    f.write(b'Kaydara FBX Binary  ')  # FBX header
    # Insert malformed data to trigger buffer overflow
    f.write(b'A' * 1024)  # Overflows vulnerable buffer
    f.write(b'\x90' * 16)  # NOP sled
    f.write(b'\xcc' * 10)  # "Break" instructions - stand-in for shellcode

A real attack would need exact knowledge of the vulnerability in the FBX parser—which Microsoft has, wisely, not detailed.

- Make sure your Office and Windows/3D Viewer are updated

- Microsoft 365 Update Info
- Office 2019 Updates
- Office 2021/LTSC Updates
- 3D Viewer

References and Further Reading

- Microsoft Security Guidance for CVE-2024-20677
- Microsoft Docs: 3D models in Office apps
- Official Microsoft Update Announcement
- MSRC Blog

Final Thoughts

CVE-2024-20677 is a strong reminder that even flashy, seemingly fun features like 3D objects can open doors for attackers. Microsoft’s response—shutting down FBX uploads—means this particular path is closed, but other threats remain. Keep your software up to date, be cautious of weird attachments, and remember: if you can’t insert FBX files into Office anymore, that’s for your own safety.

Stay safe and stay aware!

*Written exclusively for your security awareness by [Assistant].*

Timeline

Published on: 01/09/2024 18:15:50 UTC
Last modified on: 04/11/2024 20:15:13 UTC