Analysis by: Anthony Joe Melgarejo
ALIASES:

Trojan:Win32/AgentBypass.gen!K (Microsoft), Trojan.Gen.2 (Symantec), Generic.grp!ek (McAfee), Trojan-Dropper.Win32.Injector (Ikarus), Win32/AutoRun.Agent.AEP worm (ESET)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

This worm may be dropped by other malware.

As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size: 102,400 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 20 Mar 2013

Arrival Details

This worm may be dropped by the following malware:

  • TROJ_DLDR.HB

Installation

This worm drops the following files:

  • %Windows%\inf\maincom.inf
  • %System%\ntdos.inf
  • %System%\promaprt.dep

(Note: %Windows% is the Windows folder, which is usually C:\Windows.. %System% is the Windows system folder, which is usually C:\Windows\System32.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • AMrypBloodXYZFlowUSA

It injects codes into the following process(es):

  • explorer.exe

Autostart Technique

This worm 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\VmSecurity
Description = "Security Component"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\VmSecurity
DisplayName = "Security"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\VmSecurity
ErrorControl = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\VmSecurity
ImagePath = "%SystemRoot%\System32\svchost.exe -k netsvcs"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\VmSecurity
ObjectName = "LocalSystem"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\VmSecurity
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\VmSecurity
Type = "32"

It registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\VmSecurity

Other System Modifications

This worm modifies the following file(s):

  • %System%\rundll32.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

It creates the following registry entry(ies) to bypass Windows Firewall:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile
EnableFirewall = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile
DoNotAllowExceptions = "0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%Windows%\explorer.exe = "%Windows%\explorer.exe:*:Enabled:Microsoft Explorer"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%System%\svchost.exe = "%System%\svchost.exe:*:Enabled:Windows HandBook"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\GloballyOpenPorts\
List
{port number 1}:TCP = "{port number 1}:TCP:*:Enabled:@xpsp2res.dll,-2002"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\GloballyOpenPorts\
List
{port number 2}:UDP = "{port number 2}:UDP:*:Enabled:@xpsp2res.dll,-22002"

Download Routine

This worm connects to the following URL(s) to download its component file(s):

  • http://www.{BLOCKED}lower.net/document/large/msqlmem.txt
  • http://www.{BLOCKED}tcc.co.kr/bbs/images/titlebar.gif (saved as %System%\msctrll.dll)

It saves the files it downloads using the following names:

  • %System%\maincom.dll
  • %System%\maincom.inf
  • %System%\prodownq.org
  • %System%\dieharw.srgg
  • %System%\msryswt.hlp
  • %System%\sqlsrveng.dll
  • %System%\lansetting.log
  • %System%\urlsetting.log
  • %System%\msconfm.log

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

As of this writing, the said sites are inaccessible.

NOTES:

This worm skips its routine of adding a service when it finds the following processes running in the affected system:

  • explorer.exe
  • iexplore.exe
  • rundll32.exe
  • svchost.exe

It adds VMSecurity to the pool of services in the registry entry:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SvcHost netsvcs

This worm stops the service CryptSvc.

  SOLUTION

Minimum Scan Engine: 9.300
FIRST VSAPI PATTERN FILE: 9.802.02
FIRST VSAPI PATTERN DATE: 20 Mar 2013
VSAPI OPR PATTERN File: 9.803.00
VSAPI OPR PATTERN Date: 21 Mar 2013

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

Remove the malware/grayware file that dropped/downloaded WORM_STTKR.B

Step 3

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_STTKR.B. 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 4

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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • VmSecurity

Step 5

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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile
    • EnableFirewall = "1"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile
    • DoNotAllowExceptions = "0"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • %Windows%\explorer.exe = "%Windows%\explorer.exe:*:Enabled:Microsoft Explorer"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • %System%\svchost.exe = "%System%\svchost.exe:*:Enabled:Windows HandBook"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\GloballyOpenPorts\List
    • {port number 1}:TCP = "{port number 1}:TCP:*:Enabled:@xpsp2res.dll,-2002"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\GloballyOpenPorts\List
    • {port number 2}:UDP = "{port number 2}:UDP:*:Enabled:@xpsp2res.dll,-22002"

Step 6

Search and delete this file

[ Learn More ]
There may be some 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.
  • %System%\maincom.dll
  • %System%\maincom.inf
  • %System%\prodownq.org
  • %System%\dieharw.srgg
  • %System%\msryswt.hlp
  • %System%\sqlsrveng.dll
  • %System%\lansetting.log
  • %System%\urlsetting.log
  • %System%\msconfm.log

Step 7

Restart in Safe Mode

[ Learn More ]

Step 8

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.

  • rundll32.exe

Step 9

Scan your computer with your Trend Micro product to delete files detected as WORM_STTKR.B. 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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