
      ,/                                                                  ,/
    ,'/         _____                          _     _ _ _              ,'/
  ,' /         / ____|                        | |   | (_) |           ,' /
,'  /_____,   | (___   ___ _ __ ___  ___ _ __ | |__ | |_| |_ ____   ,'  /_____,
.'____    ,'   \___ \ / __| '__/ _ \/ _ \ '_ \| '_ \| | | __|_  /   .'____    ,'
     /  ,'     ____) | (__| | |  __/  __/ | | | |_) | | | |_ / /         /  ,'
    / ,'      |_____/ \___|_|  \___|\___|_| |_|_.__/|_|_|\__/___|       / ,'
   /,'                                                                 /,'
  /'                                                                  /'

Screenblitz by mightychoc
github.com/mightychoc/screenblitz

screenblitz is an addon to the Hak5 Screen Crab, a video man-in-the-middle implant. To gain access to the captured screen recordings, we either need to use the Hak5 Cloud C2 service for remote access or grab the microSD card from the device. screenblitz now offers a third option: Comfortably access your screen captures by using blitz over the Global Socket Relay Network (GSRN).

About Global Socket

Global Socket is a toolkit developed by @hackerschoice. It replaces the IP-Layer by its own Gsocket-Layer in order to allow two users to connect via TCP, even if they are behind a firewall. Gsocket uses the GSRN to connect the clients using locally derived temporary session keys and IDs based on a secret given by the user. Although you can use the GSRN for free, you can also route the traffic from your connections through your own infrastructure using Global Socket Relay. For more information on Gsocket, see the official website or the github repo.

TLDR

If you just want to get started using screenblitz quickly, follow these steps.

Adapt the config.txt file generated on the first boot of the Screen Crab. Make sure it can connect to the Internet and set CAPTURE_MODE IMAGEand STORAGE ROTATE.
Adapt SECRET, TIMEOUT and (if applicable) GSOCKET_IP inscreenblitz/.env
- SECRET defines the password used to connect the clients
- The captured files are transfered every TIMEOUT seconds
- GSOCKET_IP specifies the IP address of your self-hosted GSRN-server. Leave blank if you want to use the public GSRN.
Copy the screenblitz directory to your microSD card

Get a shell running on your crab and run:

mount -o remount,rw /dev/block/mmcblk0p1 /system
cp -r /mnt/media_rw/<your-microSD>/screenblitz /system
cd /system/screenblitz
chmod 755 install.sh
./install.sh

Wait for the installation to finish, then reboot
Connect the Screen Crab to the target device
Grab your loot using blitz -s <your-secret> -l inside your destination folder

Installation

Preparing the Screen Crab

The first thing we need is an empty microSD card, which is used to save the captured data locally, hold all necessary configuration files and to transfer the screenblitz binaries onto the crab. Make sure the card is exFAT formated, then plug it into your Screen Crab and boot the device. After approximately 30 seconds, the boot process is finished and the Crab's LED turns white. Eject the microSD card or remove it after shutting down the Screen Crab. This initial boot process generates a config.txt file on the microSD card. Open the config.txt file in your favourite text editor and edit the file like so:

Ensure that CAPTURE_MODE IMAGE and STORAGE ROTATE are set.
Choose a CAPTURE_INTERVAL (in seconds) which suits your needs.
Uncomment the WIFI_SSID and WIFI_PASS fields and enter your network credentials.

Warning

Make sure to put your credentials in quotation marks and to escape special characters (Docs).

You should end up with something like this:

#################################################################################
#             ____   ____ ____  _____ _____ _   _    ____ ____      _    ____   #
#            / ___| / ___|  _ \| ____| ____| \ | |  / ___|  _ \    / \  | __ )  #
# (\/)  (\/) \___ \| |   | |_) |  _| |  _| |  \| | | |   | |_) |  / _ \ |  _ \  #
#  ||'°°'//   ___) | |___|  _ <| |___| |___| |\  | | |___|  _ <  / ___ \| |_) | #
# ./ W  W \. |____/ \____|_| \_\_____|_____|_| \_|  \____|_| \_\/_/   \_\____/  #
#            Screen Crab by Hak5                                           v1   #
#################################################################################

LED ON
CAPTURE_MODE IMAGE
CAPTURE_INTERVAL 5
STORAGE ROTATE
BUTTON EJECT

### CONFIGURATION OPTIONS ###
# LED [ON, OFF]
#
# CAPTURE_MODE [IMAGE, VIDEO, OFF]
#   (LED indication: Image=Blue, Video=Yellow, Off=Off)
#
# DEDUPLICATE [ON, OFF]
#   (Only for IMAGE CAPTURE_MODE)
#
# CAPTURE_INTERVAL [N]
#   (in N seconds)
#
# STORAGE [ROTATE or FILL]
#
# BUTTON [EJECT, OFF]
#
# VIDEO_BITRATE [LOW, MEDIUM, HIGH]
#   (low 2Mbps, medium 4Mbps, high 16Mbps)
#
WIFI_SSID "MyWifiName"
#
WIFI_PASS "MySecretPassword"
#   (Omit WIFI_PASS for open networks)
#   (Omit BOTH WIFI_PASS and WIFI_SSID to disable wireless)
#
# ### ADDITIONAL HELP ###
# https://www.hak5.org/crab-help

Set Up `screenblitz`

The configuration of screenblitz is pretty straight forward. Once you downloaded the code, open the screenblitz/.env file in your favourite text editor and specify your desired configuration:

SECRET=<your-secret>
TIMEOUT=30
GSOCKET_IP=XXX.XXX.XXX.XXX

SECRET defines the password used to connect the clients. Default is screenblitz.
The captured files are transfered every TIMEOUT seconds. Default is 30.
GSOCKET_IP specifies the IP address of your self-hosted GSRN-server. Leave blank if you want to use the public GSRN. Default is blank.

Note

Don't confuse TIMEOUT in screenblitz/.env with the CAPTURE_INTERVAL from the Screen Crab's config.txt. CAPTURE_INTERVAL defines how often an image of the screen is saved to the microSD card. TIMEOUT defines the timeout between two synchronisations between the Crab and the listening server. So for example if CAPTURE_INTERVAL is set to 5 and and TIMEOUT is set to 30, then every thirty seconds the six pictures captured during that time will get transmitted to the listener.

Next, copy the entire screenblitz directory to the root directory of your microSD card:

cp -r screenblitz /path/to/sd-card/mountpoint

Caution

The installer script is expecting to find a directory called screenblitz on the microSD card. Make sure to copy the whole directory and not just its contents!

Set Up Folder Watcher

Before we can start using our modified Screen Crab, we need to get the listening server up and running. If you have your own GSRN-server, don't forget to specify the GSOCKET_IP before starting the listener:

#Only run this line if you have your own Gsocket relay
export GSOCKET_IP=<your-ip>

cd /path/to/destination/directory
blitz -s <your-secret> -l

Getting a Shell on the Screen Crab

In order to install screenblitz we need to have a terminal on the Screen Crab. In order to get there, start by removing the top cover of your Screen Crab (other side of where you plug in your microSD). Wire the Crab to a serial bus adapter by connecting RX <-> TX, TX <-> RX and GND <-> GND but do not yet plug the adapter into your machine. Run sudo dmesg -w on your machine and plug the adapter into your device. You should see something like this:

[100.000000] usb 1-3: new full-speed USB device number 20 using xhci_hcd
[100.000000] usb 1-3: New USB device found, idVendor=XXXX, idProduct=XXXX, bcdDevice= 6.00
[100.000000] usb 1-3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[100.000000] usb 1-3: Product: XXXX
[100.000000] usb 1-3: Manufacturer: XXXX
[100.000000] usb 1-3: SerialNumber: XXXX
[100.000000] ftdi_sio 1-3:1.0: FTDI USB Serial Device converter detected
[100.000000] usb 1-3: Detected FT232R
[100.000000] usb 1-3: FTDI USB Serial Device converter now attached to ttyUSB0

As we can see from the last line, we have a connection to the serial bus on /dev/ttyUSB0. Run sudo screen /dev/ttyUSB0 115200, then plug your microSD card into the Crab and connect it to power. You should now see the Screen Crab booting up. Again, wait for about 30 seconds until the output stops, then press Enter to see a prompt.

Check Internet Connection

On the Crab terminal, run ip a and look for an output like this:

wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
 link/ether XX:XX:XX:XX:XX:XX brd XX:XX:XX:XX:XX:XX
 inet XXX.XXX.XXX.XXX/24 brd XXX.XXX.XXX.XXX scope global wlan0
    valid_lft forever preferred_lft forever
 inet6 XXXX::XXXX:XXXX:XXXX:XXXX/64 scope link 
    valid_lft forever preferred_lft forever

To check that your connection is working, just ping -c 5 your favourite wepage. Ensure that you're able to receive packets and don't suffer any packet loss:

--- forums.hak5.com ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4000ms
rtt min/avg/max/mdev = 149.790/224.146/445.605/112.644 ms

Finish Installation

As we got an Internet connection as well as the listener up and runnning, the installation itself is pretty straight forward run the following commands to mount the file system as read-write, then copy the screenblitz directory and run install.sh:

mount -o remount,rw /dev/block/mmcblk0p1 /system
cp -r /mnt/media_rw/<your-microSD>/screenblitz /system
cd /system/screenblitz
chmod 755 install.sh
./install.sh

The install script will then copy all binaries to the dedicated place, adapt /etc/mkshrc to start the folder watcher after the boot process has finished and remount the filesystem as read-only.

After the script has finished, reboot your Screen Crab and start extracting your images.

Uninstalling `screenblitz`

If you want to revert the changes applied by install.sh, simply run uninstall.sh.

Troubleshooting

A little collection of common issues encountered when using screenblitz:

rsync: connection unexpectedly closed

If you see this message, this means that screenblitz is having troubles to find the listening party. There are multiple possibilities where this might come from:

Is the listener running?
Did you specify the -l flag on the listener?
If you are running your own GSRN-server, did you specify the GSOCKET_IP in .env on the Screen Crab? Did you define and export the variable on the listener?

mightychoc/screenblitz