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TROJ_DELF.COJ

October 09, 2012
 Analysis by: Cris Nowell Pantanilla
 PLATFORM:

Windows 2000, XP, Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW


This Trojan may be downloaded by other malware/grayware/spyware from remote sites. It may be unknowingly downloaded by a user while visiting malicious websites.

  TECHNICAL DETAILS

File Size:

539,648 bytes

File Type:

PE

Memory Resident:

Yes

Initial Samples Received Date:

25 Aug 2008

Payload:

Compromises system security

Arrival Details

This Trojan may be downloaded by other malware/grayware/spyware from remote sites.

It may be unknowingly downloaded by a user while visiting malicious websites.

It may be downloaded from the following remote sites:

  • http://{BLOCKED}kod.se/BinLadenMorto.avi_de_msn-videos.com

Installation

This Trojan drops the following files:

  • %System%\sangfox.dll - also detected as TROJ_DELF.COJ

(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 itself into the following processes as part of its memory residency routine:

  • svchost.exe

Autostart Technique

This Trojan registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\3800hk
Type = 110

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\3800hk
Start = 2

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\3800hk
ErrorControl = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\3800hk
DisplayName = system{random characters}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\3800hk
Description = system{random characters}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\3800hk
ObjectName = LocalSystem

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\3800hk
ImagePath = %System%\svchost.exe -k netsvcs

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\3800hk\Parameters
ServiceDll = %System%\sangfox.dll

It modifies the following registry entry(ies) to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SvcHost
netsvcs = {default service names}

(Note: The default value data of the said registry entry is 3800hk {default service names}.)

Backdoor Routine

This Trojan connects to the following URL(s) to send and receive commands from a remote malicious user:

  • {BLOCKED}ox.3322.org

As of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine:

8.900

FIRST VSAPI PATTERN FILE:

5.499.00

FIRST VSAPI PATTERN DATE:

25 Aug 2008

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

Restart in Safe Mode

[ Learn More ]

Step 3

Delete this registry key

[ 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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • 3800hk

Step 4

Restore this modified 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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SvcHost
    • From: netsvcs = {default service names}
      To: netsvcs = 3800HK {default service names}

Step 5

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