CVE-2023-33300 - How Command Injection in FortiNAC Lets Attackers Access Your Files

In May 2023, cybersecurity researchers disclosed a serious vulnerability affecting Fortinet FortiNAC — network access control software from Fortinet used by organizations worldwide. CVE-2023-33300 was identified as a command injection weakness, meaning an attacker could trick the system into running unauthorized commands just by sending specially crafted requests. This flaw affected FortiNAC versions 7.2.1 and earlier and 9.4.3 and earlier.

If you use FortiNAC in your network, you need to know how this works, why it’s dangerous, and what you should do right now. This post will walk you through it, with simple explanations, actual code snippets, technical details, and links to the original release.

What Is CVE-2023-33300?

CVE-2023-33300 is an “improper neutralization of special elements used in a command ('command injection')” vulnerability. In plain English, FortiNAC wasn’t carefully filtering user-supplied data sent between its internal services. That let attackers sneak special characters into commands—characters that could break out of intended scripts and execute anything the attacker wants on the system.

Fortinet’s advisory (May 9, 2023):
- PSIRT Advisory linked here

Products Affected:

FortiNAC 7.2.1 and earlier (7.x)

- Other versions may be at risk: always check the official list.

Technical Details: How the Exploit Works

FortiNAC agents talk to each other on a dedicated inter-server communications port. For efficiency, some operations allow scripts or shell commands to be run based on user-supplied input. If you don’t properly “sanitize” that input—meaning, you let through characters like ;, &&, |, or $(), you can accidentally let someone inject and run their own commands.

Vulnerable Code Example

While the actual FortiNAC code isn’t public, here’s a simple Python example to show the core mistake:

import os

user_input = get_input_from_network()
os.system("ls " + user_input)

Why is this dangerous?

If user_input = "; cat /etc/passwd;"

Then the system runs

ls ; cat /etc/passwd;

This means an attacker can run any command their account permits.

Attackers could reach internal endpoints (over the inter-server port) and pass malicious payloads.

- Only limited file access was possible—attackers couldn't directly get a shell, but they could read files they shouldn’t.

Proof of Concept: Exploit Example

Below is a simulated exploit demonstration (not real code for attack, but educational).

# Suppose there’s an internal HTTP endpoint accepting filename parameter
curl -X POST "http://fortinac-server:internal_port/getFile"; \
     -H "Content-Type: application/json" \
     -d '{"filename": "/var/log/dummy.txt; cat /etc/shadow"}'

If the backend does

subprocess.call("cat " + request["filename"], shell=True)

That command turns into

cat /var/log/dummy.txt; cat /etc/shadow

So, /etc/shadow gets sent back to the attacker.

Note: In real exploits, attackers often need to use URL-encoding, custom binaries, or bypass web application firewalls.

What Attackers Can Do

- Read critical system files (e.g., /etc/passwd, /etc/shadow)

Access files they wouldn’t otherwise have permission to see

- Use file access to gather sensitive configuration (maybe passwords, keys, or further exploit options)

How Do You Fix or Mitigate This?

Fortinet released patches. If you run FortiNAC 7.2.1, 9.4.3, or any earlier builds, update immediately to the latest version.

Mitigations

- Update to fixed versions (see here)

Original Sources & Further Reading

- Fortinet PSIRT: FG-IR-23-107
- NVD CVE-2023-33300 Entry
- Horizon3.ai FortiNAC Technical Blog (Similar Case)

Conclusion

CVE-2023-33300 is a *classic* command injection bug, but its impact on enterprise network control makes it extra dangerous. Attackers don’t need full remote access—they only need a way to hit the right port with the right syntax and can grab data from your trusted servers.

If you haven’t already patched your FortiNAC deployment, do it today—otherwise, your network (and all the devices on it) could be the next easy target.


Stay safe!
If you found this helpful, share it with your network security team today.

Timeline

Published on: 03/14/2025 16:15:27 UTC