ALIASES:

Backdoor:Win32/Zegost.BX (Microsoft); Backdoor.Trojan (Symantec); Trojan.Win32.Zegost.lt (v) (Sunbelt); Could be a Trojan horse Agent (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: 107,520 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 01 May 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 drops the following copies of itself into the affected system:

  • %Program Files%\Ruceat kqhch\Heiwwqz.exe

(Note: %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).)

It creates the following folders:

  • %Program Files%\Ruceat kqhch

(Note: %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).)

Autostart Technique

This backdoor 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\Runooi ocpokepz

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Ejzulg qacspa

Other System Modifications

This backdoor adds the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\MediaResources\msvideo

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\Runooi ocpokepz
ReleiceName = "Ejzulg qacspa"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\Ejzulg qacspa
ConnectGroup = "ĬÈÏ·Ö×é"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\Ejzulg qacspa
MarkTime = "2014-04-23 01:42"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\Ejzulg qacspa
Description = "Myqjem mjdaseso spegzskvuiq"

Dropping Routine

This backdoor drops the following files:

  • %System Root%\2256.vbs

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

Other Details

This backdoor connects to the following possibly malicious URL:

  • {BLOCKED}.102.28
  • {BLOCKED}0.1
  • {BLOCKED}.8.88
  • {BLOCKED}.233.247

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\Services
    • Runooi ocpokepz
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • Ejzulg qacspa
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\MediaResources
    • msvideo

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\SYSTEM\ControlSet001\Services\Runooi ocpokepz
    • ReleiceName = "Ejzulg qacspa"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Ejzulg qacspa
    • ConnectGroup = "ĬÈÏ·Ö×é"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Ejzulg qacspa
    • MarkTime = "2014-04-23 01:42"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Ejzulg qacspa
    • Description = "Myqjem mjdaseso spegzskvuiq"

Step 5

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 Root%\2256.vbs

Step 6

Search and delete this folder

[ 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.
  • %Program Files%\Ruceat kqhch

Step 7

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