SharpGmailC2

Our Friendly Gmail will act as Server and implant will exfiltrate data via smtp and will read commands from C2 (Gmail) via imap protocol

DISCLAIMER:

This Project doesn't work against Windows Defender after 29th of November, 2022. This tool is now signatured by MS Windows as virtool:msil/ "shgmailz." a!mtb. However, I do have plan to upgrade this project in near future, to a newer version named, SharpGmailC2V2

🚫 [Disclaimer]: Use of this project is for Educational/ Testing purposes only. Using it on unauthorised machines is strictly forbidden. If somebody is found to use it for illegal/ malicious intent, author of the repo will not be held responsible.

Setup

When setting up the intermediate sender and recipient gmail account(s), enable the POP Download and IMAP Access by following the steps in this (link)[https://support.cloudhq.net/how-to-check-if-imap-is-enabled-in-gmail-or-google-apps-account/]

Once IMAP and POP are enabled, generate an App Password by following the step in this article here. If App Password setting is not visible in Security, enable 2FA verification for the Gmail account first.

When compiling the code, update the lines that set emailToAddress, password and emailToAddress. Value for password should be set to the App Password generated in previous step. Also, note that values for emailToAddress, and emailToAddress can be the same.

Used:

1. EAGetMail library from Nuget Package Manager.
2. Costura and Costura Fody from Nuget Package Manager, in order to bundle up all the dlls altogether. This actually bulked up my implant, but for this case, I don't think that will matter much as this implant is FUD till now :).

Precautions to be taken by Operator before Using Gmail as C2:

1. Make sure the Command sent via Gmail, is in Unread Mode (if not, mark as Unread) as the implant scans the Last/latest Unread mail and checks whether it starts with "in:" or not. If it does start with "in:", it understands that, that particular textbody is a legit command, and marks that particular mail as Read and this continues till the end.

Here is the snippet:

C2 In-Action:

Quick Scan:

1. Using @matterpreter's DefenderCheck:

2. Using Antiscan.me:

3. Capa Scan:

It seems like capa is not able to detect the capabilties of my Client implant at all. But definitely creates suspicion, forcing the Malware Analyst to give the binary a second look.

4. WireShark Packet Capture:

We can see that the sent commands via Operator via Gmail and the informations that are exfiltrated/ sent out are all encrypted by Gmail's TLS encryption. On top of that, the ip address (marked) isn't suspicious at all, or in other words are OPSEC safe.

Threat Detection

SharpGmailC2 can generate following generic behaviour which can assist defenders to detect SharpGmailC2 or other processes that leverage Gmail mail protocols for Command and Control:

• Anamlous increase in DNS calls to imap.google.com and network connections to other Google domains e.g. 1e100.net.

# Monitor high network connections from a particular processID
Channel=Microsoft-Windows-Sysmon
(EventID=3 OR EventID=22)  (3=Network Connection, 22=DNS)
(DestinationHostname=*.1e100.net OR QueryName=*.gmail.com)

• Invocation of powershell process from a binary process (.dll or .exe)

Channel=Microsoft-Windows-Sysmon
EventID=1
CommandLine=powershell.exe
(ParentImage=*.exe OR ParentImage=*.dll)

Honourable Mentions:

• Got enlisted in the Golden Source of the C2 Matrix (just underneath SharpC2 by @_RastaMouse and @xpn): google_Sheet.

Credits:

1. Inspired by NamedPipes from malcomvetter.
2. Much much much thanks to @SoumyadeepBas12 for helping me out with the proper code structure of this project! 😃