Creating IDT/IDS files for IDA from MS libraries with symbols

April 22, 2016 in Malware Analysis, Reversing, Software Releases

In a reversing world it is a regular experience to come across samples that are linked to OS APIs that are imported from well-known libraries. However, on occasion we can come across files that use importing in a slightly different way – they import not via names but via ordinals. A good example are samples linking to MFC libraries.

When loaded into IDA, such samples contain lots of autogenerated function names f.ex. mfc_1234. This is pretty annoying. Of course (and luckily) there exists a lot descriptions and solutions to it – we need an IDT or an IDS file. An IDT (or its compressed version IDS) file is a ‘translator’ between ordinal numbers and actual API names – many of these exist in a default installation package of IDA, but not all… One can generate these by hand – using existing scripts – and in case the MS symbols exist for a given library – one can try to generate these automagically using a simple script I am attaching to this post.

This is the recipe:

  • Ensure your IDA is set up to use symbols from Microsoft
  • Open the MS library you analyze
  • Load its symbols from the MS web site (you are either asked, or they are loaded automatically – depends on your config)
  • When the database is fully loaded and autoanalysis is completed, launch the following script:
import idaapi
import idc
import types
import os

idt = GetIdbPath()

print "Original IDB: %s" % idt

idt = idt.replace('.idb','.idt')
idt = idt.replace('.i64','.idt')

dll = GetInputFile()

print "Saving to %s" % idt

f = open(idt, 'wb')
f.write("0 Name=%s\n" % (dll))
for i in xrange(idaapi.get_entry_qty()):
    fn = idaapi.getn_func(i)
    a = fn.startEA
    if a != BADADDR:
       eo = GetEntryOrdinal(i)
       nm = GetFunctionName(GetEntryPoint(eo))
       #cm = GetFunctionCmt(a,0)
       #print "%x: %0d, %s, %s" %  (a,eo,nm,cm)
       if nm!='':
          f.write("%d Name=%s\n" % (eo,nm))
f.close()
print "done!"
  • Now you should have the IDT file autogenerated in the same directory where the library is f.ex.
    • mfcXYZ.idb
    • mfcXYZ.idt  — this is the IDT file
  • You can now
    • Open sample linking to the MS library via ordinals
    • Load newly created IDT file
    • All mfc_1234 function names should be automatically converted to respective function/method names
  • You can also use zipids.exe to convert IDT file to IDS, but it’s not necessary

A few things about EICAR that you may be not aware of…

April 10, 2016 in Incident Response, Malware Analysis, Others, Preaching, Puzzles, Security Control, Silly

When my wife studied her MA in graphic design and branding she got a lot of interesting home work. One of them was… ‘The square’. She spent a lot of time brainstorming and eventually produced a large collection of ideas that got her a good mark. Now, the simple purpose of that exercise was to play around with the idea of… ideas. As simple as it sounds, the moment you start exploring one ‘simple’ subject you will soon find yourself deep in a forest.

As I am adding support for many Quarantine files now (to DeXRAY) I suddenly found myself in a world of Antivirus analysis. One thing that somehow connects all of AV products is not their functionality, or Utopian vision of full protection, but… the EICAR file.

I decided to explore the topic of this file a bit – same as my wife was exploring the square. Yup, here’s a boring story SLASH a bunch of ideas associated with EICAR SLASH and other topics like this …

First of all – in case you don’t know – EICAR is a small file that is used as a test for security products (in the past it was mainly antivirus, but nowadays it should apply to any security solution that looks at files/content of any sort really). Once you deploy/install the solution/product, you can drop the EICAR file all over the place and see if solution picks it up. Notably, some AV vendors apparently do not understand what EICAR’s purpose is and decided not to detect it. I won’t be pointing fingers, but upload EICAR file to VirusTotal and you will know who I am talking about.

Naming conventions in AV is a subject to many debates over many years. EICAR looks like a no-brainer though as it’s an artificial file created with a single purpose and its origin and name are well-documented. It doesn’t help though… it would seem that vendors can’t agree on one, single name. Here is a histogram of names used by AV:

EICAR_test_file                  11
EICAR-Test-File                   7
EICAR-Test-File (not a virus)     4
Eicar test file                   3
EICAR (v)                         2
Eicar-Test-Signature              2
EICAR.Test.File                   2
EICAR.TestFile                    2
EICAR Test File (NOT a Virus!)    1
EICAR.TEST.NOT-A-VIRUS            1
EICAR-Test-File (not a virus) (B) 1
EICAR Test String                 1
DOS.EiracA.Trojan                 1
Marker.Dos.EICAR.dymlmx           1
EICAR.Test.File-NoVirus           1
NORMAL:EICAR-Test-File!84776 [F]  1
EICAR-Test-File!c                 1
EICAR Test-NOT virus!!!           1
Win32.Test.Eicar.a                1
Misc.Eicar-Test-File              1
EICAR_Test                        1
NotAThreat.EICAR[TestFile]        1
qex.eicar.gen.gen                 1
TestFile/Win32.EICAR              1
Virus:DOS/EICAR_Test_File         1
EICAR-AV-Test                     1
EICAR-AV-TEST-FILE                1
EICAR-test[h]                     1

And the bonus: one of these even has a typo. Can you spot it?

EICAR is a very strange phenomenon.

It is an organization. It is a file. It has a dedicated web site. It haz a dedicated con. Its original name is inclusive of Europe, and exclusive of other continents (EICAR stands for ‘European Institute for Computer Antivirus Research’; deprecated name, but always…).

Anagrams of EICAR are ERICA, CERIA and AREIC. They serve no purpose in this article.

Properties:

File size: 68 bytes
MD5: 44D88612FEA8A8F36DE82E1278ABB02F
SHA1: 3395856CE81F2B7382DEE72602F798B642F14140
SHA256: 275A021BBFB6489E54D471899F7DB9D1663FC695EC2FE2A2C4538AABF651FD0F
CTPH: 3:a+JraNvsgzsVqSwHq9:tJuOgzsko
Entropy: 4.872327687

Eicar is a DOS file and can be executed… but only under old versions of Windows.

eicar

The source code is using the same tricks as shellcodes:

  • code is obfuscated

eicar2

  • it is a self-modifying code (patching itself)

eicar3

eicar4

Does your sandbox solution accept EICAR? Test it.

There exist tools that help you to generate EICAR file and its cousins (file formats embedding EICAR).

There exist a close friend of EICAR called AMTSO (Anti-Malware Testing Standards Organization) that focuses on testing antimalware methods. It produces some more test files to support the original idea introduced by EICAR f.ex. Potentially Unwanted Application equivalent of EICAR:

puaeicar

with the histogram of detection names as follows (VT detection rate: 43/56 – mind you that the file was compiled on 2013-04-04 21:26:07 (Thursday)):

Application.Hacktool.Amtso.A                             5
Riskware ( 0040eff71 )                                   2
AMTSO-Test                                               2
PUA_Test_File                                            2
RiskTool.EICAR-Test-File.r5 (Not a Virus)                1
RiskWare[RiskTool:not-a-virus]/Win32.EICAR-Test-File     1
RiskTool.Win32.AMTSOTestFile (not malicious)             1
Amtso.Test.Pua.A                                         1
W32/PUAtest.B                                            1
AMTSO_PUA_TEST                                           1
RiskTool.Win32!O                                         1
Application.Win32.AmtsoTest.a                            1
Riskware.AMTSO-Test-PUA                                  1
Application/AMTSOPUPTestfile                             1
Trojan.Staser.gen                                        1
Application:W32/AMTSOPUATestfile                         1
W32/TestFile.LCMA-1046                                   1
Backdoor.CPEX.Win32.29390                                1
Risktool.W32.Eicar.Test!c                                1
Hacktool.Win32.EICAR-Test-File.aa                        1
RiskTool.Win32.AMTSOTestFile                             1
not-a-virus:RiskTool.Win32.EICAR-Test-File               1
AMTSO-PUA-Test                                           1
PE:Malware.Generic/QRS!1.9E2D [F]                        1
Riskware.Win32.EICARTestFile.dmxhvk                      1
PUA.AMTSOTest                                            1
SpyCar                                                   1
PUA/AMTSO-Test                                           1
Trojan/W32.Agent.33280.TI                                1
Win32/PUAtest.B potentially unwanted                     1
W32/TestFile                                             1
Win32:AmtsoTest-A [PUP]                                  1
AMTSO-PUA-Test (PUA)                                     1
RiskTool.EICAR-Test-File.a                               1
AMTSO Test File PUA (Not a Virus!)                       1
PUP/Win32.AMTSO_Test                                     1

…and the cloudish EICAR file as well. Here’s the histogram of names given to the cloudish EICAR file (only 23/56 vendors detect it on VT; compilation date:  2010-07-08 23:02:46 (Thursday), ouch!):

AMTSO_TEST_CLOUDCAR                    2
Cldcar-Test!3FB121FBBCCB               2
Trojan.Win32.Generic!BT                2
Trojan.Agent/Gen-CloudTest             1
Virus:DOS/EICAR_Test_File              1
Trojan.Generic                         1
Application.Win32.CloudTest.s          1
Win.Trojan.11584714-1                  1
Amtso.Test.Cloudcar.A                  1
Trojan.Brodcom.Win32.366               1
Trojan.Win32.DangerousObject.dlgbhn    1
AMTSO-CLOUD-Test                       1
Trojan.Win32.Z.Agent.7178[h]           1
CLOUDCAR_Test                          1
UDS:DangerousObject.Multi.Generic      1
DangerousObject.Multi.Generic!c        1
W32/GenBl.3FB121FB!Olympus             1
Mal/Generic-S                          1
AMTSO Test File (NOT a Virus!)         1
Trj/CI.A                               1

There also exist a close friend fo EICAR called GTUBE (Generic Test for Unsolicited Bulk Email) for testing anti-spam solutions. It is also 68 bytes long.

Last, but not least – there exists a shorter version of EICAR and it is 12 bytes SHORTER than the original!

The Base64-encoded EICAR looks like this:

WDVPIVAlQEFQWzRcUFpYNTQoUF4pN0NDKTd9JDIDYOUSPOTTHISEVJQ0FSLVNUQU5EQVJELUFOVElWSVJVUy1URVNU
LUZJTEUhJEgrSCo=

You may come across it as it is being used in various tests and… it is a method used by Esafe to save Quarantine files. And… maybe you can’t read this post in case your security product is over protective and detected the BASE64-encoded EICAR string. Well, if it does… it shouldn’t, as I included ‘DIDYOUSPOTTHIS’ in the BASE64 encoding above. Well, did you spot that DIDYOUSPOTTHIS?

EICAR is a tool. I use it to test Quarantine files’ encryption. When I find no encryption, or trivial encryption/encoding – I love EICAR. When I have to dig into some actual code to find out how they transform the original EICAR bytes into sth terrible I absolutely hate this little piece of hybrid data/code ;).