Hi Guys,

This particular writeup is about how I was able to find a publically accessible Jenkin instance in a private bugbounty program and leverage it to perform Remote Code Execution (RCE).

Every hack, every pentesting starts with recon (information gathering) so this - finding subdomain, open ports/services, public server IPs are some parts of it. In order to find public server IPs, one of the tools I generally rely on is https://censys.io/.

Censys has a great ability of finding IP addresses and gathering information about them. Censys also come to help in order to discover internal tools and assets by analyzing the SSL certificate, ports open etc.

When I searched the targeted domain on the same (let's call it as redacted.com as it was a private program, the name can’t be disclosed), I found an instance running on 8080 port —

Censys Result

As it can be seen, server name here was Jetty:8080 which gave me a glimpse that it might have Jenkins running on it (usually because it’s running on a standard port 80/443/8080/8443 on Jetty)- What is Jenkins- It is used as a CI-Continous Integration tool, used for automating the deployment of projects/applications in enterprises. I further checked the IP (X.X.X.X) for more details and it was indeed Jenkins running there —

Jenkins running

I opened it and it was publically accessible and the worst part was it didn’t have any authentication set over it.

Jenkins dashboard

As you can see, I was able to access Jenkins dashboard, getting access to Jenkins dashboard in itself is a security concern. An attacker can access AWS Access keys, sensitive API tokens, private keys, Server’s pem files, IP addresses, usernames and email address etc. How much disaster it can cause, read this!

Having worked closely with the CI team, I was aware of plenty of stuff related to Jenkins like to view all the people having access of Jenkins Instance /asynchPeople/ provides that —

Jenkins User Access

/credentials/ — it gives access to view credential ids, names. /configure/ — it is a configuration management dashboard for Jenkins. /configureSecurity/ — configuration management for security settings. /script/ — script console to run commands.

Now it’s time to check the same here, without thinking much I tried to see whether I have sufficient permission to access /script/ or not and to all my luck, I had it —

/script/ accessible leading to Remote Code Execution (local server image)

As it can be seen, I tried to read “/etc/passwd” and I was able to do so. Similarly, I could write any file, upload file etc.

Since Jenkins also has the availability to hook up Git plugin which enables running Git commands from the console itself.

GitHub Plugin

So, the publicly accessible Jenkins console enabled me to view and modify the production code of the application also and that’s made it more dangerous!

And this is what all can happen when companies mistakenly make the Jenkins server accessible over the internet and don’t have proper authentication set over it thinking it’s an internal application.