BKDR_GOODOOR.ASU

 Analysis by: Oliver Ramirez

 ALIASES:

Backdoor.Goodor (NORTON)

 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 executes commands from a remote malicious user, effectively compromising the affected system.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size:

2,371,584 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

07 Sep 2017

Payload:

Terminates processes, Connects to URLs/IPs, Downloads files, Executes files

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 and executes the following files:

  • %Application Data%\NT\ntdll.exe
  • %Application Data%\NT\ntdll.exe.cmd

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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 creates the following registry entries to enable automatic execution of dropped component at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
ntdll = "%Application Data%\NT\ntdll.exe" ddd-d7f6f50cae6c789223e174690fe5c567

Backdoor Routine

This Backdoor executes the following commands from a remote malicious user:

  • Terminates running process.
  • Download and execute files.

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • http://{BLOCKED}.{BLOCKED}.10.193/aspnet_client/system_web/4_0_30319/update/DefaultForm.txt
  • http://{BLOCKED}.{BLOCKED}.157.34/aspnet_client/system_web/4_0_30319/update/DefaultForm.txt
  • http://{BLOCKED}.{BLOCKED}.11.130/aspnet_client/system_web/4_0_30319/update/DefaultForm.txt
  • http://{BLOCKED}.{BLOCKED}.188.18/aspnet_client/system_web/4_0_30319/update/DefaultForm.txt
  • http://{BLOCKED}.{BLOCKED}.10.158/aspnet_client/system_web/4_0_30319/update/DefaultForm.txt
  • http://{BLOCKED}.{BLOCKED}.61.221/aspnet_client/system_web/4_0_30319/update/DefaultForm.txt
  • http://{BLOCKED}.{BLOCKED}.49.115/aspnet_client/system_web/4_0_30319/update/DefaultForm.txt
  • http://{BLOCKED}.{BLOCKED}.199.197/aspnet_client/system_web/4_0_30319/update/DefaultForm.txt
  • http://{BLOCKED}.{BLOCKED}.143.107/aspnet_client/system_web/4_0_30319/update/DefaultForm.txt

Other Details

This Backdoor deletes itself after execution.

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

13.644.08

FIRST VSAPI PATTERN DATE:

07 Sep 2017

VSAPI OPR PATTERN File:

13.645.00

VSAPI OPR PATTERN Date:

08 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

Identify and terminate files detected as BKDR_GOODOOR.ASU

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • ntdll = "%Application Data%\NT\ntdll.exe" ddd-d7f6f50cae6c789223e174690fe5c567

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.  
  • %Application Data%\NT\ntdll.exe.cmd
  • %Application Data%\NT\ntdll.exe

Step 6

Scan your computer with your Trend Micro product to delete files detected as BKDR_GOODOOR.ASU. 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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