Analysis by: Kathleen Notario
ALIASES:

Trojan.Dropper (Symantec); TrojanDropper:Win32/Dunik!rts (Microsoft); Trojan.Win32.Agent.gbya (Kaspersky); Mal/Ovoxual-A (Sophos)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

This backdoor connects to a certain site. Depending on the server's reply it may perform certain commands.

This backdoor may be dropped by other malware.

It does not have any propagation routine.

It does not have any downloading capability.

  TECHNICAL DETAILS

File Size: 139,264 bytes
Memory Resident: Yes
Initial Samples Received Date: 14 Sep 2011
Payload: Connects to URLs/IPs

Arrival Details

This backdoor may be dropped by the following malware:

  • TROJ_DROPPER.YRK

Installation

This backdoor drops the following files:

  • %Application Data%\FAVORITES.DAT - non-malicious file
  • %Application Data%\msupdater.exe - also detected as BKDR_DUNIK.AA

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.)

It adds the following processes:

  • %System%\svchost.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

It injects codes into the following process(es):

  • %System%\svchost.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "Explorer.exe "%Application Data%\msupdater.exe""

Propagation

This backdoor does not have any propagation routine.

Download Routine

This backdoor does not have any downloading capability.

NOTES:

It connects to the following site:

  • {BLOCKED}4.{BLOCKED9.140.212

Depending on the server's reply it may perform the following commands:

  • Create a process
  • Check connection
  • Sleep
  • List running processes
  • Terminate process
  • Count files and directories in %Windows%
  • Set current directory
  • Create a file
  • Write to a file
  • Copy a file
  • Delete a file
  • Get host name
  • Enumerate network resource

  SOLUTION

Minimum Scan Engine: 9.200
VSAPI OPR PATTERN File: 8.457.00
VSAPI OPR PATTERN Date: 27 Sep 2011

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Remove the malware/grayware file that dropped/downloaded BKDR_DUNIK.AA

Step 3

Identify and delete files detected as BKDR_DUNIK.AA using either the Startup Disk or Recovery Console

[ 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 NT\CurrentVersion\Winlogon
    • Shell = Explorer.exe %Application Data%\msupdater.exe

Step 5

Search and delete this file

[ Learn More ]
There may be some component 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.
  • %Application Data%\FAVORITES.DAT

Step 6

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