BKDR_HDOOR.A

June 10, 2015
 Analysis by: Joachim Suico
 ALIASES:

Backdoor.Gwapoors (Symantec); Gen:Trojan.Heur.D.wGWad0rsPrpi (F-Secure); HEUR:Trojan.Win32.Generic (Kaspersky)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Dropped by other malware, Downloaded from the Internet

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 runs certain commands that it receives remotely from a malicious user. Doing this puts the affected computer and information found on the computer at greater risk.

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

369,152 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

13 Jan 2015

Payload:

Compromises system security

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 Profile%\Common Files\NT\Lib\winhost.exe (If affected user is administrator)
  • %User Profile%\System\winhost.exe (Otherwise)

(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.)

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
Microsoft Messenger = "%User Profile%\System\winhost.exe" (If affected user is NOT administrator)

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\winhost (If affected user is administrator)

Other System Modifications

This backdoor creates the following registry entry(ies) to bypass Windows Firewall:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\GloballyOpenPorts\
List
143:TCP = "143:TCP:*:Enabled:{Chinese characters}"

Backdoor Routine

This backdoor opens the following port(s) where it listens for remote commands:

  • 143

It executes the following command(s) from a remote malicious user:

  • Disconnect backdoor connection
  • Get malware install path
  • Enumerate directories/files
  • Type a txt file content
  • Execute a program
  • Open a CMD shell
  • Load and unload a dll
  • Upload and download a file

Other Details

This backdoor deletes the initially executed copy of itself

  SOLUTION

Minimum Scan Engine:

9.750

FIRST VSAPI PATTERN FILE:

11.710.06

FIRST VSAPI PATTERN DATE:

13 Jan 2015

VSAPI OPR PATTERN File:

11.711.00

VSAPI OPR PATTERN Date:

14 Jan 2015

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.

  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\winhost

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\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\GloballyOpenPorts\List
    • 143:TCP = "143:TCP:Enabled:{Chinese characters}"
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • Microsoft Messenger = "%User Profile%\System\winhost.exe"

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_HDOOR.A. 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 7

Scan your computer with your Trend Micro product to delete files detected as BKDR_HDOOR.A. 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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