Web-based management interfaces are widely used to simplify network device management. However, they sometimes introduce security risks if user inputs are not properly validated. A good example is CVE-2022-20656, a serious vulnerability affecting Cisco’s Prime Infrastructure (Cisco PI) and Evolved Programmable Network Manager (Cisco EPNM).

In this long read, we’ll walk you through what this vulnerability is, how it can be exploited, and, most importantly, how to protect your systems.

What is CVE-2022-20656?

CVE-2022-20656 is a path traversal vulnerability in the web-based management interfaces of Cisco PI and Cisco EPNM. It allows an authenticated, remote attacker to write arbitrary files anywhere on the host system by manipulating the URL within the HTTPS request.

Why is Path Traversal Dangerous?

Path traversal (sometimes called directory traversal) is a method that lets attackers access files and directories that should not be accessible from the web interface. By using special characters like ../, an attacker can “traverse” the directory structure and potentially overwrite, delete, or read sensitive files.

If the application expects a request like

https://target-server/upload?filename=report.txt

And does not clean the user input, an attacker could send

https://target-server/upload?filename=../../../../tmp/hacked.txt

If not properly handled, this might write or overwrite files outside the intended folder.

How Does the Cisco Vulnerability Work?

The Cisco PI and EPNM web interfaces failed to properly check the filename when a user uploads or writes data. This allowed a logged-in attacker to use directory traversal sequences.

Attacker logs in with valid credentials.

2. Sends a crafted HTTPS request containing directory traversal sequences (../) in the URL or form-data.

Proof-of-Concept

While the exact endpoints may differ across Cisco’s versions, a generic code snippet to illustrate the problem could look like this (Python example using requests):

import requests

# Credentials of an existing user
username = "admin"
password = "supersecret"

# Server details
url = "https://target-cisco-server/web-interface/path";

# Malicious path traversal payload
data = {
    "filename": "../../../../../tmp/evil.txt",
    "content": "This is attacker data"
}

# Send the malicious request
response = requests.post(
    url,
    auth=(username, password),
    data=data,
    verify=False # For testing only!
)

print(response.status_code)

Warning: This code is for educational purposes only. Do not use it without permission or in a production environment.

Real-World Risks

- Creating web shells: If the attacker can write executable files into web-accessible directories, they could install a web shell for persistent access.

Overwriting configuration: Attackers can corrupt system files or place backdoors.

- Escalating attacks: If other vulnerabilities exist, attackers could chain exploits (e.g., privilege escalation, data exfiltration).

Mitigation and Fixes

Cisco has acknowledged the vulnerability and released software updates to fix the issue. There are no known workarounds.

References

- NIST NVD: CVE-2022-20656
- Cisco Security Advisory (original)
- Directory traversal attack (OWASP)

Conclusion

CVE-2022-20656 shows how insufficient input validation can lead to risky vulnerabilities, even in enterprise-grade products like Cisco PI and EPNM. If you haven't patched these systems, do so now. For defenders, always keep management interfaces off the public internet and restrict access as much as possible.

Staying proactive is your best defense against these and future flaws.

Timeline

Published on: 11/15/2024 16:15:21 UTC
Last modified on: 11/18/2024 17:11:56 UTC