Analysis by: Mark Joseph Manahan
 PLATFORM:

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

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This backdoor arrives as an attachment to email messages spammed by other malware/grayware or malicious users. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It executes then deletes itself afterward.

  TECHNICAL DETAILS

File Size: 561,152 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 05 Apr 2013

Arrival Details

This backdoor arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

It 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 backdoor drops the following files:

  • %User Profile%\Application Data\{random 4}.reg
  • %User Profile%\Application Data\mcp.ico
  • %User Profile%\Application Data\Mozilla\Firefox\Profiles\{random}\searchplugins\search.xml
  • %Desktop%\Computer.lnk
  • %User Temp%\{random 3}.sys
  • %User Temp%\{random 1}.exe
  • %User Temp%\{random number}.tmp
  • %User Temp%\{random 2}.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.. %Desktop% is the current user's desktop, which is usually C:\Documents and Settings\{User Name}\Desktop on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\Desktop on Windows Vista and 7.. %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, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

It drops the following copies of itself into the affected system:

  • %User Profile%\Application Data\ScanDisc.exe
  • %User Profile%\Application Data\{random name}.exe
  • %User Temp%\{Random Number}.tmp

(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.. %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, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

It executes then deletes itself afterward.

Autostart Technique

This backdoor creates the following registry entries to enable automatic execution of dropped component at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
{random name} = "%User Profile%\Application Data\{random name}.exe"

Other System Modifications

This backdoor adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
ConsentPromptBehaviorAdmin = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
ConsentPromptBehaviorUser = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
EnableLUA = "0"

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows
update = "shortcut"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Tcpip\Parameters\
Interfaces\{GUID}
NameServer = "8.8.8.8"

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

Other Details

This backdoor connects to the following possibly malicious URL:

  • {BLOCKED}.{BLOCKED}.12.201
  • {BLOCKED}.{BLOCKED}.243.62
  • {BLOCKED}.{BLOCKED}.83.116
  • {BLOCKED}.{BLOCKED}.38.174
  • {BLOCKED}t.{BLOCKED}u7my179mywsku.com
  • {BLOCKED}1.{BLOCKED}string.com

NOTES:

It appends the legitimate file %User Profile%\Application Data\Mozilla\Firefox\Profiles\{random}\prefs.js with user_pref(&"browser.search.selectedEngine&"_http://{BLOCKED}la.com/?&uid={number}&q={searchTerms}");.

  SOLUTION

Minimum Scan Engine: 9.300
FIRST VSAPI PATTERN FILE: 9.838.04
FIRST VSAPI PATTERN DATE: 05 Apr 2013
VSAPI OPR PATTERN File: 9.839.00
VSAPI OPR PATTERN Date: 06 Apr 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

Scan your computer with your Trend Micro product and note files detected as BKDR_SIMDA.KB

Step 3

Restart in Safe Mode

[ Learn More ]

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\RunOnce
    • {random name} = "%User Profile%\Application Data\{random name}.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • ConsentPromptBehaviorAdmin = "0"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • ConsentPromptBehaviorUser = "0"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • EnableLUA = "0"
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows
    • update = "shortcut"

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\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{GUID}
    • From: NameServer = "8.8.8.8"
      To: NameServer = ""

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.
  • %User Profile%\Application Data\{random 4}.reg
  • %User Profile%\Application Data\mcp.ico
  • %User Profile%\Application Data\Mozilla\Firefox\Profiles\{random}\searchplugins\search.xml
  • %Desktop%\Computer.lnk
  • %User Temp%\{random 3}.sys
  • %User Temp%\{random 1}.exe
  • %User Temp%\{random number}.tmp
  • %User Temp%\{random 2}.exe

Step 7

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

NOTES:

Before proceeding to Step 7, do the following steps to remove the strings added by the malware/grayware/spyware in the file %User Profile%\Application Data\Mozilla\Firefox\Profiles\{random}\prefs.js file:

  1. Open the file %User Profile%\Application Data\Mozilla\Firefox\Profiles\{random}\prefs.js using a text editor such as Notepad.
  2. Find and delete the following entry:
    • user_pref(&"browser.search.selectedEngine&"_http://{BLOCKED}la.com/?&uid={number}&q={searchTerms}");
  3. Save the file then close the text editor.


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