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BKDR_ZEGOST.NZU

September 20, 2017
 Analysis by: John Anthony Banes
 ALIASES:

Backdoor.Win32.Zegost.mtfci (Kaspersky)

 PLATFORM:

Windows

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

  • 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 the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

90,112 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

30 Aug 2017

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 and executes them:

  • %User Temp%\logicfax.exe

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp 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.)

Autostart Technique

This Backdoor registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\FontSrv
Type = 272

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\FontSrv
Start = 2

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\FontSrv
ErrorControl = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\FontSrv
ImagePath = "%User Temp%\logicfax.exe"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\FontSrv
DisplayName = "Windows Font"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\FontSrv\Security
Security = {hex values}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\FontSrv
ObjectName = "LocalSystem"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\FontSrv
Description = "Manages fonts for Windows-based programs. If this service is stopped, audio devices and effects will not work."

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

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
(Default) = "%User Temp%\logicfax.exe"

It 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\FontSrv

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\FontSrv\Security

Other Details

This Backdoor connects to the following possibly malicious URL:

  • vertify.{BLOCKED}u.net

It deletes the initially executed copy of itself

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

13.656.02

FIRST VSAPI PATTERN DATE:

13 Sep 2017

VSAPI OPR PATTERN File:

13.657.00

VSAPI OPR PATTERN Date:

14 Sep 2017

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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • FontSrv

Step 5

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
    • (Default) = "%User Temp%\logicfax.exe"

Step 6

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