BKDR_TEAMBOT.DLL

 Analysis by: Michael Jay Villanueva

 ALIASES:

Trojan:Win32/Dynamer!ac (Microsoft); Backdoor.NSIS.Agent.p (Kaspersky); Backdoor.Teambot (Symantec)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • 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 connects to a website to send and receive information. However, as of this writing, the said sites are inaccessible.

It modifies Internet Explorer security settings. This puts the affected computer at greater risk, as it allows malicious URLs to be accessed by the computer.

  TECHNICAL DETAILS

File Size:

3,233,227 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

02 Jun 2016

Payload:

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 files:

  • %Application Data%\Div\avicap32.dll -> Detected as BKDR_TEAMBOT.DLL
  • %Application Data%\Div\cfmon.exe
  • %Application Data%\Div\cfmon.lnk
  • %Application Data%\Div\tv_w32.dll
  • %Application Data%\Div\tv_w32.exe
  • %Application Data%\Div\tv_x64.dll
  • %Application Data%\Div\installvpn.pg
  • %Application Data%\Div\rdw.pg
  • %Application Data%\Div\scankey.pg
  • %Application Data%\Div\tv.cfg
  • %Application Data%\Div\update.pg
  • %Application Data%\Div\TeamViewer_Desktop.exe
  • %Application Data%\Div\TeamViewer_Resource_en.dll
  • %Application Data%\Div\x64\install64.exe
  • %Application Data%\Div\x64\teamviewervpn.sys
  • %Application Data%\Div\x64\TeamViewerVPN.inf
  • %Application Data%\Div\x64\teamviewervpn.cat
  • %Application Data%\Div\x86\install.exe
  • %Application Data%\Div\x86\teamviewervpn.sys
  • %Application Data%\Div\x86\TeamViewerVPN.inf
  • %Application Data%\Div\x86\teamviewervpn.cat
  • %User Temp%\{random filename 1}
  • %User Temp%\{random filename 2}
  • %User Temp%\{random filename 3}.jpg
  • %User Temp%\nst{random}.tmp\{random filename 4}
  • %User Temp%\nst{random}.tmp\System.dll
  • %User Temp%\nst{random}.tmp\nsExec.dll

(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.. %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.)

It creates the following folders:

  • %Application Data\Div
  • %User Temp%\nst{random}.tmp

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

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
cfmon = C:\Documents and Settings\dyituser_xp32\Application Data\Div\cfmon.exe

Backdoor Routine

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

  • http://{BLOCKED}aamfg.info/gfblegh/update.php?id={unique ID}&stat={value}

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

Web Browser Home Page and Search Page Modification

This backdoor modifies Internet Explorer zone settings.

NOTES:

This backdoor can execute the following commands which is received over HTTPS:

  • Connects to a specified host server
  • Download and execute component files
  • Download configuration and updates
  • Download updated copy of itself
  • Maintains the connection
  • Steals information
  • Terminates the connection

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

12.574.04

FIRST VSAPI PATTERN DATE:

07 Jun 2016

VSAPI OPR PATTERN File:

12.575.00

VSAPI OPR PATTERN Date:

08 Jun 2016

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

Remove the malware/grayware file dropped/downloaded by BKDR_TEAMBOT.DLL. (Note: Please skip this step if the threat(s) listed below have already been removed.)

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
    • cfmon = C:\Documents and Settings\dyituser_xp32\Application Data\Div\cfmon.exe

Step 6

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %Application Data\Div
  • %User Temp%\nst{random}.tmp

Step 7

Search and delete these files

[ 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%\Div\avicap32.dll
  • %Application Data%\Div\cfmon.exe
  • %Application Data%\Div\cfmon.lnk
  • %Application Data%\Div\tv_w32.dll
  • %Application Data%\Div\tv_w32.exe
  • %Application Data%\Div\tv_x64.dll
  • %Application Data%\Div\installvpn.pg
  • %Application Data%\Div\rdw.pg
  • %Application Data%\Div\scankey.pg
  • %Application Data%\Div\tv.cfg
  • %Application Data%\Div\update.pg
  • %Application Data%\Div\TeamViewer_Desktop.exe
  • %Application Data%\Div\TeamViewer_Resource_en.dll
  • %Application Data%\Div\x64\install64.exe
  • %Application Data%\Div\x64\teamviewervpn.sys
  • %Application Data%\Div\x64\TeamViewerVPN.inf
  • %Application Data%\Div\x64\teamviewervpn.cat
  • %Application Data%\Div\x86\install.exe
  • %Application Data%\Div\x86\teamviewervpn.sys
  • %Application Data%\Div\x86\TeamViewerVPN.inf
  • %Application Data%\Div\x86\teamviewervpn.cat
  • %User Temp%\{random filename 1}
  • %User Temp%\{random filename 2}
  • %User Temp%\{random filename 3}.jpg
  • %User Temp%\nst{random}.tmp\{random filename 4}
  • %User Temp%\nst{random}.tmp\System.dll
  • %User Temp%\nst{random}.tmp\nsExec.dll

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_TEAMBOT.DLL. 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 9

Reset Internet security settings

[ Learn More ]


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