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BKDR_VAWTRAK.YXC

November 04, 2014
 Analysis by: RonJay Kristoffer Caragay
 ALIASES:

Backdoor:Win32/Vawtrak.F (Microsoft); RDN/Generic Dropper!vk (McAfee); Trojan.Gen (Symantec); Trojan-Dropper.Win32.Dapato.epyg (Kaspersky); Troj/Agent-AJIL (Sophos); Trojan horse SHeur4.CCXI (AVG)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size:

415,344 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

13 Oct 2014

Arrival Details

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Autostart Technique

This backdoor adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random 1} = "regsvr32.exe "%All Users Profile%\Application Data\{random 1}\{random 1}.dat""

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CLASSES_ROOT\CLSID\{CLSID 1}

HKEY_CLASSES_ROOT\CLSID\{CLSID 2}

HKEY_CURRENT_USER\Software\Classes\
CLSID\{CLSID 1}

HKEY_CURRENT_USER\Software\Classes\
CLSID\{CLSID 2}

It adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\Main
NoProtectedModeBanner = "1"

HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\Main
TabProcGrowth = "0"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings\
Zones\3
2500 = "3"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings
GlobalUserOffline = "0"

HKEY_CLASSES_ROOT\CLSID\{CLSID 1}
#cert = "31"

HKEY_CLASSES_ROOT\CLSID\{CLSID 1}
#sd = "{hex value}"

HKEY_CLASSES_ROOT\CLSID\{CLSID 2}
{CLSID 3} = "{hex values}"

HKEY_CLASSES_ROOT\CLSID\{CLSID 2}
{CLSID 4} = "{hex values}"

HKEY_CURRENT_USER\Software\Classes\
CLSID\{CLSID 1}
#cert = "31"

HKEY_CURRENT_USER\Software\Classes\
CLSID\{CLSID 1}
#sd = "{hex value}"

HKEY_CURRENT_USER\Software\Classes\
CLSID\{CLSID 2}
{CLSID 3} = "{hex values}"

HKEY_CURRENT_USER\Software\Classes\
CLSID\{CLSID 2}
{CLSID 4} = "{hex values}"

Dropping Routine

This backdoor drops the following files:

  • %All Users Profile%\Application Data\{random 1}\{random 1}.dat

(Note: %All Users Profile% is the All Users folder, where it usually is C:\Documents and Settings\All Users on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\ProgramData on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

Other Details

This backdoor connects to the following possibly malicious URL:

  • {BLOCKED}ta.com
  • {BLOCKED}tek.com
  • {BLOCKED}rs.com
  • {BLOCKED}a.com
  • {BLOCKED}te.com
  • {BLOCKED}r.com

It deletes itself after execution.

  SOLUTION

Minimum Scan Engine:

9.700

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Close all opened browser windows

Step 5

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {random 1} = "regsvr32.exe "%All Users Profile%\Application Data\{random 1}\{random 1}.dat""
  • In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main
    • NoProtectedModeBanner = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main
    • TabProcGrowth = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3
    • 2500 = "3"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
    • GlobalUserOffline = "0"

Step 6

Search and delete these files

[ Learn More ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.  
  • %All Users Profile%\Application Data\{random 1}\{random 1}.dat

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_VAWTRAK.YXC. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.

Step 8

The following created files/folders/registry keys/registry entries cannot be identified by the user since there are no reference values in the created key. The only way it can be identified is by comparing the present system information with a backup. Note that the said components do not have to be deleted since it won't be harmful to the system.

 
  • HKEY_CLASSES_ROOT\CLSID
    • {CLSID 1}
  • HKEY_CLASSES_ROOT\CLSID
    • {CLSID 2}
  • HKEY_CURRENT_USER\Software\Classes\CLSID
    • {CLSID 1}
  • HKEY_CURRENT_USER\Software\Classes\CLSID
    • {CLSID 2}


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