TROJ_SMALLTR.AFK


 ALIASES:

Trojan:Win32/VB.SX (Microsoft); Generic Dropper.eh (McAfee); Trojan Horse (Symantec); Trojan.Win32.Generic.pak!cobra (Sunbelt); Trojan.Generic.2073653 (FSecure)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • 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.

  TECHNICAL DETAILS

File Size:

282,624 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

20 Sep 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 creates the following folders:

  • %User Profile%\Microsoft\HTML Help

(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.)

Autostart Technique

This Trojan 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%\twext.exe,"

(Note: The default value data of the said registry entry is %Windows%\system32\userinit.exe,.)

Other System Modifications

This Trojan deletes the following files:

  • %System%\twext.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 adds the following registry keys:

HKEY_CURRENT_USER\software\microsoft\
windows\currentversion\explorer\
{00D0FD7F-DCFF-FC00-F399-837C709A807C}

HKEY_CURRENT_USER\software\microsoft\
windows\currentversion\explorer\
{02000000-DCFF-FC00-F399-837C709A807C}

HKEY_CURRENT_USER\software\microsoft\
windows\currentversion\explorer\
{D0090000-DCFF-FC00-F399-837C709A807C}

HKEY_CURRENT_USER\Software\Microsoft\
ActiveMovie\devenum\{4EFE2452-168A-11D1-BC76-00C04FB9453B}

HKEY_CURRENT_USER\Software\Microsoft\
ActiveMovie\devenum\{4EFE2452-168A-11D1-BC76-00C04FB9453B}\
Default MidiOut Device

HKEY_CURRENT_USER\Software\Microsoft\
ActiveMovie\devenum\{E0F158E1-CB04-11D0-BD4E-00A0C911CE86}

HKEY_CURRENT_USER\Software\Microsoft\
ActiveMovie\devenum\{E0F158E1-CB04-11D0-BD4E-00A0C911CE86}\
Default DirectSound Device

HKEY_CURRENT_USER\Software\Microsoft\
Multimedia\ActiveMovie\Filter Cache

It adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
ActiveMovie\devenum\{4EFE2452-168A-11D1-BC76-00C04FB9453B}\
Default MidiOut Device
FriendlyName = "Default MidiOut Device"

HKEY_CURRENT_USER\Software\Microsoft\
ActiveMovie\devenum\{4EFE2452-168A-11D1-BC76-00C04FB9453B}\
Default MidiOut Device
CLSID = "{07B65360-C445-11CE-AFDE-00AA006C14F4}"

HKEY_CURRENT_USER\Software\Microsoft\
ActiveMovie\devenum\{4EFE2452-168A-11D1-BC76-00C04FB9453B}\
Default MidiOut Device
FilterData = "{random values}"

HKEY_CURRENT_USER\Software\Microsoft\
ActiveMovie\devenum\{4EFE2452-168A-11D1-BC76-00C04FB9453B}\
Default MidiOut Device
MidiOutId = "ffffffff"

HKEY_CURRENT_USER\Software\Microsoft\
ActiveMovie\devenum\{E0F158E1-CB04-11D0-BD4E-00A0C911CE86}\
Default DirectSound Device
FriendlyName = "Default DirectSound Device"

HKEY_CURRENT_USER\Software\Microsoft\
ActiveMovie\devenum\{E0F158E1-CB04-11D0-BD4E-00A0C911CE86}\
Default DirectSound Device
CLSID = "{79376820-07D0-11CF-A24D-0020AFD79767}"

HKEY_CURRENT_USER\Software\Microsoft\
ActiveMovie\devenum\{E0F158E1-CB04-11D0-BD4E-00A0C911CE86}\
Default DirectSound Device
FilterData = "{random values}"

HKEY_CURRENT_USER\Software\Microsoft\
ActiveMovie\devenum\{E0F158E1-CB04-11D0-BD4E-00A0C911CE86}\
Default DirectSound Device
DSGuid = "{00000000-0000-0000-0000-000000000000}"

HKEY_CURRENT_USER\Software\Microsoft\
Multimedia\ActiveMovie\Filter Cache
0 = "{random values}"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
MediaPlayer
MP2.SaveDir = "%Program Files%\Windows Media Player"

(Note: The default value data of the said registry entry is %Program Files%\Windows Media Player.)

It deletes the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\MUILanguages\
FileVersions

Dropping Routine

This Trojan drops the following files:

  • %User Temp%\5fe1.exe
  • %User Temp%\5fe2.avi
  • %User Profile%\HTML Help\hh.dat
  • %System%\twext.exe

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.. %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.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}hoff.com/temp/1cfg.bin

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine:

9.200

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_SMALLTR.AFK using either the Startup Disk or Recovery Console

[ 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_CURRENT_USER\software\microsoft\windows\currentversion\explorer
    • {00D0FD7F-DCFF-FC00-F399-837C709A807C}
  • In HKEY_CURRENT_USER\software\microsoft\windows\currentversion\explorer
    • {02000000-DCFF-FC00-F399-837C709A807C}
  • In HKEY_CURRENT_USER\software\microsoft\windows\currentversion\explorer
    • {D0090000-DCFF-FC00-F399-837C709A807C}
  • In HKEY_CURRENT_USER\Software\Microsoft\ActiveMovie\devenum
    • {4EFE2452-168A-11D1-BC76-00C04FB9453B}
  • In HKEY_CURRENT_USER\Software\Microsoft\ActiveMovie\devenum\{4EFE2452-168A-11D1-BC76-00C04FB9453B}
    • Default MidiOut Device
  • In HKEY_CURRENT_USER\Software\Microsoft\ActiveMovie\devenum
    • {E0F158E1-CB04-11D0-BD4E-00A0C911CE86}
  • In HKEY_CURRENT_USER\Software\Microsoft\ActiveMovie\devenum\{E0F158E1-CB04-11D0-BD4E-00A0C911CE86}
    • Default DirectSound Device
  • In HKEY_CURRENT_USER\Software\Microsoft\Multimedia\ActiveMovie
    • Filter Cache

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\ActiveMovie\devenum\{4EFE2452-168A-11D1-BC76-00C04FB9453B}\Default MidiOut Device
    • FriendlyName = "Default MidiOut Device"
  • In HKEY_CURRENT_USER\Software\Microsoft\ActiveMovie\devenum\{4EFE2452-168A-11D1-BC76-00C04FB9453B}\Default MidiOut Device
    • CLSID = "{07B65360-C445-11CE-AFDE-00AA006C14F4}"
  • In HKEY_CURRENT_USER\Software\Microsoft\ActiveMovie\devenum\{4EFE2452-168A-11D1-BC76-00C04FB9453B}\Default MidiOut Device
    • FilterData = "{random values}"
  • In HKEY_CURRENT_USER\Software\Microsoft\ActiveMovie\devenum\{4EFE2452-168A-11D1-BC76-00C04FB9453B}\Default MidiOut Device
    • MidiOutId = "ffffffff"
  • In HKEY_CURRENT_USER\Software\Microsoft\ActiveMovie\devenum\{E0F158E1-CB04-11D0-BD4E-00A0C911CE86}\Default DirectSound Device
    • FriendlyName = "Default DirectSound Device"
  • In HKEY_CURRENT_USER\Software\Microsoft\ActiveMovie\devenum\{E0F158E1-CB04-11D0-BD4E-00A0C911CE86}\Default DirectSound Device
    • CLSID = "{79376820-07D0-11CF-A24D-0020AFD79767}"
  • In HKEY_CURRENT_USER\Software\Microsoft\ActiveMovie\devenum\{E0F158E1-CB04-11D0-BD4E-00A0C911CE86}\Default DirectSound Device
    • FilterData = "{random values}"
  • In HKEY_CURRENT_USER\Software\Microsoft\ActiveMovie\devenum\{E0F158E1-CB04-11D0-BD4E-00A0C911CE86}\Default DirectSound Device
    • DSGuid = "{00000000-0000-0000-0000-000000000000}"
  • In HKEY_CURRENT_USER\Software\Microsoft\Multimedia\ActiveMovie\Filter Cache
    • 0 = "{random values}"

Step 5

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\MediaPlayer
    • From: MP2.SaveDir = "%Program Files%\Windows Media Player"
      To: MP2.SaveDir = ""%Program Files%\Windows Media Player""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: userinit = "%System%\userinit.exe,%System%\twext.exe,"
      To: userinit = ""%Windows%\system32\userinit.exe,""

Step 6

Search and delete these files

[ 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.
  • %User Temp%\5fe1.exe
  • %User Temp%\5fe2.avi
  • %User Profile%\HTML Help\hh.dat
  • %System%\twext.exe

Step 7

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %User Profile%\Microsoft\HTML Help

Step 8

Scan your computer with your Trend Micro product to delete files detected as TROJ_SMALLTR.AFK. 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 9

Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %System%\twext.exe

Step 10

Restore these deleted registry keys/values from backup

*Note: Only Microsoft-related keys/values will be restored. If the malware/grayware also deleted registry keys/values related to programs that are not from Microsoft, please reinstall those programs on your computer.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\MUILanguages
    • FileVersions


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