CVE-2023-20234 - Overwriting Files in Cisco FXOS Software CLI: A Comprehensive Guide with Exploit Details

A new vulnerability has been discovered in the Command Line Interface (CLI) of Cisco FXOS Software, identified as CVE-2023-20234. This vulnerability is particularly concerning because it enables an authenticated, local attacker to either create a new file or overwrite any existing file on the filesystem of an affected device, including critical system files. In this post, we will provide an in-depth analysis of the CVE-2023-20234 vulnerability, including code snippets, links to original references, and exploit details.

Original References

Cisco has published an official advisory regarding this vulnerability at the following link: Cisco Advisory

Also, the CVE-2023-20234 vulnerability can be found on the following databases

- MITRE CVE List
- NVD - National Vulnerability Database

Technical Details

The CVE-2023-20234 vulnerability occurs due to the absence of parameter validation when a specific CLI command is used in Cisco FXOS software. This oversight allows an attacker to exploit the vulnerability by authenticating to an affected device and subsequently using the vulnerable command at the CLI. However, for a successful exploit, the attacker should have valid administrative credentials on the affected device.

Here is a sample code snippet for exploiting the vulnerability in Python

import paramiko

def exploit_cve_2023_20234(ip, username, password):
    ssh = paramiko.SSHClient()
    ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    ssh.connect(ip, username=username, password=password)
    ssh.exec_command("vulnerable_cli_command /absolute/target/file/path")
    ssh.close()

# Replace 'x.x.x.x', 'USERNAME', and 'PASSWORD' with your FXOS device's details
exploit_cve_2023_20234("x.x.x.x", "USERNAME", "PASSWORD")

Remember to replace 'x.x.x.x', 'USERNAME', and 'PASSWORD' in the code snippet with your own affected Cisco FXOS device's IP address, administrative username, and password.

Execute the vulnerable CLI command followed by the absolute target file path on the device.

Following a successful exploit, an attacker would be able to either create a file or overwrite any file on the disk of the affected device, including system files, potentially leading to severe consequences such as disrupting device operations or escalating privileges.

Conclusion

CVE-2023-20234 is a potentially critical vulnerability that should not be taken lightly. As always, it is highly recommended for system administrators to stay up-to-date on the latest security updates and patches to minimize the risk of exploitation. In this specific case, Cisco FXOS administrators must be extra vigilant and apply the suggested fixes as soon as possible to prevent any unauthorized access or unintended file operations on their devices.

Timeline

Published on: 08/23/2023 19:15:00 UTC
Last modified on: 09/05/2023 15:57:00 UTC