Analysis by: Jeanne Jocson
ALIASES:

Backdoor:Win32/Vawtrak!rfn (Microsoft)

 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 the initially executed copy of itself.

  TECHNICAL DETAILS

File Size: 191,430 bytes
File Type: DLL
Memory Resident: Yes
Initial Samples Received Date: 21 Mar 2016

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.

Installation

This backdoor drops a copy of itself in the following folders using different file names:

  • %ProgramData%\{random name}\{random file name}.dll (For Windows Vista or higher)
  • %Application Data%\{random name}\{random file name}.dll (For Windows XP or lower)

(Note: %ProgramData% is the Program Data folder, where it usually is C:\Program Files in Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\ProgramData in 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.. %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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.)

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 numbers} = "regsvr32.exe "%Application Data%\{random name}\{random file name}.dll""%Application Data%\{random name}\{random file name}.dll (For Windows XP or lower)

HKCU\Software\Microsoft\
Windows\CurrentVersion\Run
{random numbers} = "regsvr32.exe "%ProgramData%\{random name}\{random file name}.dll"" (For Windows Vista or higher)

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\{CLSID}\
{random name}\{random numbers} (For Windows XP or lower)

HKEY_CURRENT_USER\Software\{CLSID}\
{CLSID}(For Windows Vista or higher)

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\{CLSID}\
{random name}\{random numbers} (For Windows XP or lower)
{random 4 letters} = "{hex values}"

HKEY_CURRENT_USER\Software\{CLSID}\
{CLSID} (For Windows Vista or higher)
{random 4 letters} = "{hex values}"

Other Details

This backdoor deletes the initially executed copy of itself

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 12.416.05
FIRST VSAPI PATTERN DATE: 21 Mar 2016
VSAPI OPR PATTERN File: 12.417.00
VSAPI OPR PATTERN Date: 22 Mar 2016

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

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 numbers} = "regsvr32.exe "%Application Data%\{random name}\{random file name}.dll""%Application Data%\{random name}\{random file name}.dll
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {random numbers} = "regsvr32.exe "%ProgramData%\{random name}\{random file name}.dll""

Step 5

Delete this registry key

[ Learn More ]

=Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator’s help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software
    • {CLSID}

Step 6

Reset Internet security settings

[ Learn More ]

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_VAWTRAK.YUYJJ. 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.


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