BKDR_COREBOT.A

 Analysis by: David John Agni

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel:

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 creates folders where it drops its files.

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

It connects to certain websites to send and receive information. However, as of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size:

645,632 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

09 Sep 2015

Payload:

Steals information, Connects to URLs/IPs

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:

  • %AppDataLocal%\Microsoft\{GUID 2}\{GUID}.exe

(Note: %AppDataLocal% is the Application Data folder found in Local Settings, where it is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local 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.)

It adds the following processes:

  • svchost.exe
  • dllhost.exe - watchdog

It creates the following folders:

  • %AppDataLocal%\Microsoft\{GUID 1}
  • %AppDataLocal%\Microsoft\{GUID 2}

(Note: %AppDataLocal% is the Application Data folder found in Local Settings, where it is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local 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.)

It injects codes into the following process(es):

  • Created processes

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{GUID 3} = "%AppDataLocal%\Microsoft\{GUID 2}\{GUID}.exe"

Backdoor Routine

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

  • Download and Execute file
  • Load and unload downloaded plugin
  • Start and Stop plugin
  • Perform Remote Shell
  • Update URL list
  • Update itself
  • Update Plugin
  • Modify Config
  • Manage File
  • Manage MBR
  • Send gathered data

Information Theft

This backdoor gathers the following data:

  • List Infected Processes
  • Malware Information
  • Plugin Information
  • Victim Machine Information

Stolen Information

The stolen information is saved in the following file:

  • {Created Folder}\{random file name}.dmp

Other Details

This backdoor connects to the following website to send and receive information:

  • http://{BLOCKED}zo-sorelli.com/client
  • http://{BLOCKED}mhyfuhg.ddns.net/verify
  • http://{DGA}.{BLOCKED}s.net/verify

However, as of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine:

9.750

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 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
    • {GUID 3} = "%AppDataLocal%\Microsoft\{GUID 2}\{GUID}.exe"

Step 5

The following created files/folders/registry keys/registry entries cannot be identified by the user since there are no reference values in the created key. The only way it can be identified is by comparing the present system information with a backup. Note that the said components do not have to be deleted since it won't be harmful to the system.

  • %AppDataLocal%\Microsoft\{GUID 1}
  • %AppDataLocal%\Microsoft\{GUID 2}

Step 6

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