BKDR_ZEGOST.AI

June 18, 2013
 ALIASES:

TrojanDownloader:Win32/Somex.B (Microsoft); PWS-TravNet-FBCS!ECAB0435810D (McAfee); Trojan.Gen.2 (Symantec); Trojan.Win32.Agent2.fitq (Kaspersky); Trojan horse Agent3.BZKU (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.

  TECHNICAL DETAILS

File Size:

303,616 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

14 Jun 2013

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.

Other System Modifications

This backdoor modifies the following file(s):

  • %Windows%\Prefetch\NTOSBOOT-B00DFAAD.pf
  • %Windows%\Prefetch\WUAUCLT.EXE-399A8E72.pf

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

It deletes the following files:

  • %Windows%\SoftwareDistribution\DataStore\Logs\edbtmp.log

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

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\6to4
Type = "12"

(Note: The default value data of the said registry entry is 20.)

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\6to4\Parameters
ServiceDll = "%System%\6to4ex.dll"

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

Dropping Routine

This backdoor drops the following files:

  • %System Root%\net.exe
  • %System%\config_shenghai.dat
  • temp.bat
  • %System%\6to4ex.dll

(Note: %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.)

Other Details

This backdoor connects to the following possibly malicious URL:

  • http://www.{BLOCKED}eacess.com/fi/dochunter.asp?{random characters}

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

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\SYSTEM\ControlSet001\Services\6to4
    • From: Type = "12"
      To: Type = ""20""
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\6to4\Parameters
    • From: ServiceDll = "%System%\6to4ex.dll"
      To: ServiceDll = ""{random values}""

Step 3

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.
  • %System Root%\net.exe
  • %System%\config_shenghai.dat
  • temp.bat
  • %System%\6to4ex.dll

Step 4

Scan your computer with your Trend Micro product to delete files detected as BKDR_ZEGOST.AI. 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 5

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\NTOSBOOT-B00DFAAD.pf
    • %Windows%\Prefetch\WUAUCLT.EXE-399A8E72.pf

Step 6

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.

  • %Windows%\SoftwareDistribution\DataStore\Logs\edbtmp.log


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