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.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 268,332 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 22 Aug 2013

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.

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
dtwtkd = "regsvr32.exe /s %User Profile%\Application Data\dtwtkd.dat"

Other System Modifications

This Trojan modifies the following file(s):

  • %Windows%\Prefetch\CMD.EXE-087B4001.pf

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

It adds the following registry keys:

HKEY_CURRENT_USER\SOFTWARE\AppDataLow\
{6DC27B69-71ED-4D68-A596-26246E600862}

HKEY_CURRENT_USER\SOFTWARE\AppDataLow\
{117A5899-70DC-4EA0-B35F-15F35AEF383F}

It adds the following registry entries:

HKEY_CURRENT_USER\Software\AppDataLow\
{6DC27B69-71ED-4D68-A596-26246E600862}
{70F02777-377A-401E-81D9-18A6337C4BAD} = "{random values}"

HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\Main
NoProtectedModeBanner = "1"

HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\Main
TabProcGrowth = "0"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings\
Zones\3
2500 = "3"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\Safer\
CodeIdentifiers
DefaultLevel = "4"

(Note: The default value data of the said registry entry is 40000.)

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\Safer\
CodeIdentifiers
TransparentEnabled = "1"

(Note: The default value data of the said registry entry is 1.)

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\Safer\
CodeIdentifiers
PolicyScope = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\Safer\
CodeIdentifiers
ExecutableTypes = "WSC"

(Note: The default value data of the said registry entry is {random values}.)

Dropping Routine

This Trojan drops the following files:

  • %User Profile%\Application Data\dtwtkd.dat
  • %Windows%\Prefetch\ATTRIB.EXE-39EAFB02.pf

(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.. %Windows% is the Windows folder, which is usually C:\Windows.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}cconverter.biz
  • http://{BLOCKED}cconverter.biz/4vir/antispyware/loadadv.exe

It deletes itself after execution.

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine: 9.300

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

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_CURRENT_USER\SOFTWARE\AppDataLow
    • {6DC27B69-71ED-4D68-A596-26246E600862}
  • In HKEY_CURRENT_USER\SOFTWARE\AppDataLow
    • {117A5899-70DC-4EA0-B35F-15F35AEF383F}

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\Windows\CurrentVersion\Run
    • dtwtkd = "regsvr32.exe /s %User Profile%\Application Data\dtwtkd.dat"
  • In HKEY_CURRENT_USER\Software\AppDataLow\{6DC27B69-71ED-4D68-A596-26246E600862}
    • {70F02777-377A-401E-81D9-18A6337C4BAD} = "{random values}"
  • In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main
    • NoProtectedModeBanner = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main
    • TabProcGrowth = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3
    • 2500 = "3"

Step 5

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Safer\CodeIdentifiers
    • From: DefaultLevel = "4"
      To: DefaultLevel = ""40000""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Safer\CodeIdentifiers
    • From: TransparentEnabled = "1"
      To: TransparentEnabled = ""1""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Safer\CodeIdentifiers
    • PolicyScope = "0"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Safer\CodeIdentifiers
    • From: ExecutableTypes = "WSC"
      To: ExecutableTypes = ""{random values}""

Step 6

Search and delete these components

[ Learn More ]
There may be some components 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 Profile%\Application Data\dtwtkd.dat
  • %Windows%\Prefetch\ATTRIB.EXE-39EAFB02.pf

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_KRYPTK.PPL. 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 8

Restore deleted/modified files and/or registry entries from backup

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

    • %Windows%\Prefetch\CMD.EXE-087B4001.pf


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