Analysis by: Jaime Benigno Reyes

ALIASES:

Trojan.Win32.Staser.asfs (Kaspersky)

 PLATFORM:

Windows

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

  • 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: 300,032 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 11 Dec 2014

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 files:

  • %Application Data%\麽鎒駓覜
  • %System%\config\systemprofile\AppData\Roaming\麽鎒駓覜
  • %Windows%\FrameworkUpdate\Update.exe

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.. %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

Other System Modifications

This Trojan adds the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SystemUpdate

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SystemUpdate
Type = "16"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SystemUpdate
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SystemUpdate
ErrorControl = "0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SystemUpdate
ImagePath = "%Windows%\FrameworkUpdate\Update.exe"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SystemUpdate
DisplayName = "Enables the detection, download and installation of updates for Windows."

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SystemUpdate
ObjectName = "LocalSystem"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Security Center
cval = "0"

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\MpsSvc
ErrorControl = "0"

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\MpsSvc
Start = "4"

(Note: The default value data of the said registry entry is "2".)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SharedAccess
ErrorControl = "0"

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\wscsvc
ErrorControl = "0"

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\wscsvc
Start = "4"

(Note: The default value data of the said registry entry is "2".)

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}archresults.com/?aff=7581&saff=9181

  SOLUTION

Minimum Scan Engine: 9.700
FIRST VSAPI PATTERN FILE: 11.338.02
FIRST VSAPI PATTERN DATE: 11 Dec 2014
VSAPI OPR PATTERN File: 11.339.00
VSAPI OPR PATTERN Date: 12 Dec 2014

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

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

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.

 
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services
    • SystemUpdate

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\Security Center
    • From: cval = "0"
      To: cval = "1"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\MpsSvc
    • From: ErrorControl = "0"
      To: ErrorControl = "1"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\MpsSvc
    • From: Start = "4"
      To: Start = "2"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\SharedAccess
    • From: ErrorControl = "0"
      To: ErrorControl = "1"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\wscsvc
    • From: ErrorControl = "0"
      To: ErrorControl = "1"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\wscsvc
    • From: Start = "4"
      To: Start = "2"

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.
  • %Application Data%\麽鎒駓覜
  • %System%\config\systemprofile\AppData\Roaming\麽鎒駓覜
  • %Windows%\FrameworkUpdate\Update.exe

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_KRYPTIK.ACD. 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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