TROJ_DELF.YQ

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

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

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

It connects to certain URLs. It may do this to remotely inform a malicious user of its installation. It may also do this to download possibly malicious files onto the computer, which puts the computer at a greater risk of infection by other threats.

  TECHNICAL DETAILS

File Size:

31,744 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

13 Jan 2012

Arrival Details

This Trojan 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 Trojan drops the following copies of itself into the affected system:

  • %User Profile%\userlog.exe
  • %System%\crrss.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.. %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 Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
userlog = "%User Profile%\userlog.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Winlogon
shell = "explorer.exe "%User Profile%\userlog.exe""

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
crrss = "%System%\crrss.exe"

It modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Userinit = "%System%\userinit.exe,%System%\crrss.exe"

(Note: The default value data of the said registry entry is "%System%\userinit.exe,".)

Other System Modifications

This Trojan adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\wuvlpmihvbgicywkcqnuncncxcbgvf
mjrwolemxecgnhnwdupelphfgvrvwg = {blank}

Download Routine

This Trojan connects to the following malicious URLs:

  • http://feed911.com/gate.php?ch=1
  • http://feed911.com/gate.php?u=18

NOTES:
As of this writing, however, no file can be downloaded.

  SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

8.704.10

FIRST VSAPI PATTERN DATE:

13 Jan 2012

VSAPI OPR PATTERN File:

8.705.00

VSAPI OPR PATTERN Date:

13 Jan 2012

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

Identify and delete files detected as TROJ_DELF.YQ using either the Startup Disk or Recovery Console

[ Learn More ]

Step 3

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
    • userlog = "%User Profile%\userlog.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
    • shell = "explorer.exe "%User Profile%\userlog.exe""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • crrss = "%System%\crrss.exe"

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\Winlogon
    • From: Userinit = "%System%\userinit.exe,%System%\crrss.exe"
      To: Userinit = "%System%\userinit.exe,"

Step 5

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_CURRENT_USER\Software
    • wuvlpmihvbgicywkcqnuncncxcbgvf

Step 6

Scan your computer with your Trend Micro product to delete files detected as TROJ_DELF.YQ. 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.

NOTES:

Recommendation:

  1. This malware is detected and removed by the latest Trend Micro anti-malware engine and pattern. Always keep pattern files and engines up-to-date. To know more about updating your Trend Micro product’s pattern, please refer to this Trend Micro support page.
    Note: The steps apply for specific products indicated in the page.

    To actively detect and protect your machine, enable real-time scanning of your Trend Micro anti-malware product. Refer to the following Trend Micro support page to know more about enabling real-time scanning in your Trend Micro product:

  2. Enable firewall to protect against threats.
  3. Be aware of social engineering attacks.
  4. Avoid accessing the listed malicious URLs to prevent possible re-infection.
  5. Monitor network connections for any suspicious connection or connectivity.
  6. Regularly update list of sites that are trusted.


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