Whether it be through phishing, or some other means, waiting for your incoming beacons can be an anxious moment. Every time I send off phishing e-mails, I anxiously await to receive the incoming beacons. I personally want to know and be alerted the second that I receive a beacon, so I figured this would be a great time to work with Raphael Mudge’s scripting language that’s built right into Cobalt Strike – Aggressor.
Aggressor is an event-driven language, very similar to scripts people may have developed for IRC. One of the events built into Aggressor is “beacon_initial“. This event is triggered when a beacon is established for the first time. Using this event, you can have Cobalt Strike do “something” when a beacon first checks in.
Aggressor is based on the language Sleep (also by Raphael Mudge) which supports an “exec” function. So to tie this all together, we can have Aggressor run a command when each new beacon first checks in. Sounds like I can just write a script that texts me with some of the information I’m interested in receiving for each new beacon!
The Aggressor script can be found here, so let’s go through this and learn what’s happening.
on beacon_initial {
local('$computer');
local('$internal');
$computer = beacon_info($1, "computer");
$internal = beacon_info($1, "internal");
exec("/root/cobaltstrike/emailme.py --ip " . $internal . " --computer '" . $computer . "'");
}
The “beacon_initial” is the event that triggers when a beacon first checks in. The “local” commands are used to declare the contained string as a local variable. These will store the internal IP and computer name of the beacon that just checked in. The “beacon_info” commands allows us to retrieve metadata about the incoming beacon, in this case the internal IP and computer name. Finally, the “exec” command executes the script at the location I’ve specified. Now, all that is needed is a script that sends the text messages!
This can be easily done using Python, and I have a script here that does it.
#!/usr/bin/env python
import argparse
import smtplib
from email.MIMEMultipart import MIMEMultipart
from email.MIMEText import MIMEText
parser = argparse.ArgumentParser(description='beacon info')
parser.add_argument('--computer')
parser.add_argument('--ip')
args = parser.parse_args()
fromaddr = ""
toaddr = ["7777777777@txt.att.net", "8888888888@vtext.com"]
msg = MIMEMultipart()
msg['From'] = fromaddr
msg['To'] = ", ".join(toaddr)
msg['Subject'] = "INCOMING BEACON"
hostname = args.computer
internal_ip = args.ip
body = "Check your teamserver! \nHostname - " + hostname + "\nInternal IP - " + internal_ip
msg.attach(MIMEText(body, 'plain'))
server = smtplib.SMTP('smtp.gmail.com', 587)
server.starttls()
server.login(fromaddr, "")
text = msg.as_string()
server.sendmail(fromaddr, toaddr, text)
server.quit()
This script was modified from another script I found online. It uses gmail (you will need to provide a username and password) to send e-mails to addresses that you specify. In this case, it’s sends e-mails to the addresses for AT&T and Verizon that translates e-mails to text messages (just change the phone numbers in the toad variable). Now, anytime that I receive an incoming beacon, this script is triggered and I receive a text message containing the hostname and internal ip of the compromised system!
You can run this one of two ways. While connected to your team server, just load up the Script Console, load your script, and you’re good to go. However, this obviously requires you to stay connected to your team server. Your other option is to use the “agscript” binary that comes with Cobalt Strike. This program lets you connect to a team server and run a script, without requiring the Cobalt Strike client. An easy way to use this is to SSH to your team server, start a screen session, and run the agscript binary in the background with the above Aggressor script. Now, anytime you receive a beacon, your Aggressor script will trigger your e-mail script which texts you to notify you of the new beacon!
