Analysis by: Christopher Daniel So

ALIASES:

VirTool:Win32/Obfuscator.NI (Microsoft), W32.Changeup!gen9 (Symantec), Downloader-CJX.gen.o (McAfee), Trojan.Win32.VB.ankz (Kaspersky), Worm.Win32.Autorun.xy (Sunbelt)W32/VB.BT.gen!Eldiradi (FProt), Win32/AutoRun.VB.XY worm (Nod32), TR/Dropper.Gen (AntiVir), Win32/VBCrypt (AVG), W32/VB.BT.gen!Eldorado (Authentium)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Propagates via removable drives, Propagates via network drives

This worm arrives by connecting affected removable drives to a system. It arrives by accessing affected shared networks.

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

  TECHNICAL DETAILS

File Size: 61,440 bytes
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 10 Feb 2011

Arrival Details

This worm arrives by connecting affected removable drives to a system.

It arrives by accessing affected shared networks.

Installation

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

  • %User Profile%\{random file name}.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random file name} = "%User Profile%\{random file name}.exe /{random character}"

Propagation

This worm drops copies of itself in network drives such as the following:

  • {drive letter}:\{random file name}.exe
  • {drive letter}:\{random file name}x.exe

It drops the following copy(ies) of itself in all removable drives:

  • {drive letter}:\{random file name}.exe
  • {drive letter}:\{random file name}x.exe

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

[{random characters}]
[AUtorun]
{random characters}
shellexecute={random file name}.exe
{random characters}
ICon=%systemROot%\sYStem32\shelL32.dlL,4
{random characters}
uSEAuTOPlAy=1
{random characters}
[{random characters}]
{random characters}

Other Details

This worm does the following:

  • It hides folders in removable and network drives, and drops .LNK files with the names of the hidden folders in removable and network drives that point to the dropped copy {random file name}x.exe.

  SOLUTION

Minimum Scan Engine: 8.900
FIRST VSAPI PATTERN FILE: 7.828.16
FIRST VSAPI PATTERN DATE: 11 Feb 2011

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

Identify and terminate files detected as WORM_AUTORUN.SM4

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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
    • {random file name}=%User Profile%\{random file name}.exe /{random character}

Step 4

Search and delete AUTORUN.INF files created by WORM_AUTORUN.SM4 that contain these strings

[ Learn More ]
[{random characters}]
[AUtorun]
{random characters}
shellexecute={random file name}.exe
{random characters}
ICon=%systemROot%\sYStem32\shelL32.dlL,4
{random characters}
uSEAuTOPlAy=1
{random characters}
[{random characters}]
{random characters}

Step 5

Scan your computer with your Trend Micro product to delete files detected as WORM_AUTORUN.SM4. 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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