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BKDR_ZEGOST.LDY

April 24, 2014
 ALIASES:

Backdoor:Win32/Zegost.AD, TrojanProxy:Win32/Potukorp.A (Microsoft); Trojan.FakeAV (Symantec); Mal/EncPk-GT (Sophos); Packed.Win32.Krap.c (fs) (Sunbelt); Win32/Heur.dropper (AVG)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW


This backdoor 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:

125,440 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

24 Apr 2014

Arrival Details

This backdoor 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 creates the following folders:

  • %Windows%\A7C74F29
  • %User Temp%\62250
  • %User Temp%\62250\....
  • %User Temp%\62281
  • %User Temp%\62281\....

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

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
A7C74F29 = "%Windows%\A7C74F29\svchsot.exe"

Other System Modifications

This backdoor modifies the following file(s):

  • %System%\drivers\etc\hosts

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

It deletes the following files:

  • %User Temp%\62250\TemporaryFile\TemporaryFile

(Note: %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 deletes the following folders:

  • %User Temp%\62250\TemporaryFile
  • %User Temp%\62281\TemporaryFile

(Note: %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 adds the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\MediaResources\msvideo

HKEY_LOCAL_MACHINE\SYSTEM\InfoTime

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\policies\
Explorer\Run

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\InfoTime
InfoTime = "20140411"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Explorer\Run
jinyo = "%Program Files%\Common Files\Updater.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings
DnsCacheEnabled = "0"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings
DnsCacheTimeout = "0"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings
ServerInfoTimeOut = "0"

Dropping Routine

This backdoor drops the following files:

  • %User Temp%\Binder.exe
  • %User Temp%\Updater.exe
  • %System Root%\koreaautoup.bmp
  • %System%\drivers\etc\hosts.ics
  • %Windows%\A7C74F29\svchsot.exe
  • %Program Files%\Common Files\Updater.exe

(Note: %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.. %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.. %System% is the Windows system folder, which is usually C:\Windows\System32.. %Windows% is the Windows folder, which is usually C:\Windows.. %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000, Server 2003, and XP (32-bit), Vista (32-bit), and 7 (32-bit), or C:\Program Files (x86) in Windows XP (64-bit), Vista (64-bit), and 7 (64-bit).)

Other Details

This backdoor connects to the following possibly malicious URL:

  • http://user.{BLOCKED}e.qq.com/2091757018

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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\MediaResources
    • msvideo
  • In HKEY_LOCAL_MACHINE\SYSTEM
    • InfoTime
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\policies\Explorer
    • Run

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • A7C74F29 = "%Windows%\A7C74F29\svchsot.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\InfoTime
    • InfoTime = "20140411"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\Explorer\Run
    • jinyo = "%Program Files%\Common Files\Updater.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
    • DnsCacheEnabled = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
    • DnsCacheTimeout = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
    • ServerInfoTimeOut = "0"

Step 5

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 Temp%\Binder.exe
  • %User Temp%\Updater.exe
  • %System Root%\koreaautoup.bmp
  • %System%\drivers\etc\hosts.ics
  • %Windows%\A7C74F29\svchsot.exe
  • %Program Files%\Common Files\Updater.exe

Step 6

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %Windows%\A7C74F29
  • %User Temp%\62250
  • %User Temp%\62250\....
  • %User Temp%\62281
  • %User Temp%\62281\....

Step 7

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

    • %System%\drivers\etc\hosts

Step 9

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.

  • %User Temp%\62250\TemporaryFile\TemporaryFile


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