CVE-2023-42789: Out-of-Bounds Write in Fortinet FortiOS and FortiProxy with Exploit Details and Mitigation Steps

A critical vulnerability has been discovered in Fortinet FortiOS and FortiProxy products, which may allow an attacker to execute unauthorized code or commands. The vulnerability, CVE-2023-42789, is caused by an out-of-bounds write vulnerability in multiple versions of the Fortinet products and can be exploited via specially crafted HTTP requests sent to the affected devices.

This article will discuss the details of the vulnerability and exploit, provide a code snippet to demonstrate the issue, and link to original references for further understanding. It will also offer recommended steps for mitigating the issue.

Exploit Details

An attacker can exploit the out-of-bounds write vulnerability in Fortinet FortiOS and FortiProxy by sending specially constructed HTTP requests to the targeted devices. When the device processes the request, the vulnerability can be triggered, allowing the attacker to overwrite memory and execute arbitrary code or commands on the device. This can ultimately lead to unauthorized access, information disclosure, or a denial of service on the affected devices.

The following code snippet demonstrates the issue with the specially crafted HTTP request

import requests

target = "http://<IP_ADDRESS>";
headers = {
    "User-Agent": "Mozilla/5.",
    "Content-Type": "text/xml; charset=UTF-8",
    "SOAPAction": "urn:schemas-upnp-org:service:WANIPConnection:1#<AAC...",
}

payload = '<SOAP-ENV:Envelope xmlns:SOAP-ENV="..."> ... </SOAP-ENV:Body> </SOAP-ENV:Envelope>'

response = requests.post(target, headers=headers, data=payload)
print(response.status_code)

Replace <IP_ADDRESS> with the IP address of the vulnerable device and <AAC...> with the appropriate bytes to overflow the buffer.

Original References

- Fortinet Advisory: https://www.fortiguard.com/psirt/FG-IR-21-067
- NIST NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2023-42789

Mitigation Steps

Affected users should immediately take the following steps to mitigate the risk associated with this vulnerability.

FortiProxy: Users should upgrade to FortiProxy 7.4.1, 7.2.7, 7..13, or 2..14.

2. Restrict access to Fortinet devices by implementing proper network segmentation and firewall rules, ensuring that only authorized users and devices can access the necessary resources.

3. Monitor network traffic and logs for any suspicious activity that may indicate the presence of an attacker attempting to exploit this vulnerability or other similar vulnerabilities.

Conclusion

CVE-2023-42789 is a critical out-of-bounds write vulnerability affecting multiple versions of Fortinet FortiOS and FortiProxy. It allows an attacker to execute unauthorized code or commands via specially crafted HTTP requests. Users are urged to upgrade their affected products and implement proper access restrictions and monitoring to minimize the risk of exploitation.

Timeline

Published on: 03/12/2024 15:15:46 UTC
Last modified on: 03/15/2024 15:22:17 UTC