BKDR_BANDOK.SM

 Analysis by: Sabrina Lei Sioting

 ALIASES:

TrojanProxy:Win32/Dosenjo.A (Microsoft), Backdoor.Win32.Bandok.it (Kaspersky), Trojan.Adclicker (Symantec), W32/Bandok.IT!tr.bdr (Fortinet), W32/BackdoorX.ARIV (Fprot), Backdoor.Win32.Bandok (Ikarus),

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • 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.

As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size:

67,072 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

30 Oct 2010

Payload:

Downloads 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 the following copies of itself into the affected system:

  • %System Root%\Documents and Settings\All Users\Application Data\csrss.exe

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It drops the following non-malicious file:

  • %System Root%\Documents and Settings\All Users\Application Data\loggy.txt

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • BabloPobejdaetZlo2

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
Svchost = "%System Root%\Documents and Settings\All Users\Application Data\csrss.exe"

Other System Modifications

This backdoor adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion
SvchostID = "{machine ID converted}"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion
SvchostVersion = "{number}"

HKEY_USERS\.DEFAULT\SOFTWARE\
Microsoft\Windows\CurrentVersion
SvchostVersion = "{number}"

It adds the following registry keys as part of its installation routine:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Servers

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\GloballyOpenPOrts\
List
110:TCP = "110:TCP:*:Enabled:svchost"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%System Root%\Documents and Settings\All Users\Application Data\csrss.exe = "%System Root%\Documents and Settings\All Users\Application Data\csrss:*:Enabled:svchost"

Download Routine

This backdoor connects to the following URL(s) to download its component file(s):

  • http://{BLOCKED}lero.com/s.html?cachingDeny={random characters}&id={converted machine ID}
  • http://{BLOCKED}stats.ru/s.html?cachingDeny={random characters}&id={converted machine ID}
  • http://{BLOCKED}tats.ru/s.html?cachingDeny={random characters}&id={converted machine ID}
  • http://{BLOCKED}ler.com/s.html?cachingDeny={random characters}&id={converted machine ID}
  • http://{BLOCKED}-ana1itics.com/s.html?cachingDeny={random characters}&id={converted machine ID}
  • http://{BLOCKED}machiner.com/s.html?cachingDeny={random characters}&id={converted machine ID}

It saves the files it downloads using the following names:

  • %User Temp%\csrss5.dll
  • %System%\csrss5.dll

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.. %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

As of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine:

9.300

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Identify and terminate files detected as BKDR_BANDOK.SM

[ Learn More ]
  1. 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.
  2. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 3

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion
    • Servers

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
    • Svchost = "%System Root%\Documents and Settings\All Users\Application Data\csrss.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion
    • SvchostID = "{machine ID converted}"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion
    • SvchostVersion = "{number}"
  • In HKEY_USERS\.DEFAULT\SOFTWARE\Microsoft\Windows\CurrentVersion
    • SvchostVersion = "{number}"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • %System Root%\Documents and Settings\All Users\Application Data\csrss.exe = "%System Root%\Documents and Settings\All Users\Application Data\csrss:*:Enabled:svchost"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\GloballyOpenPOrts\List
    • 110:TCP = "110:TCP:*:Enabled:svchost"

Step 5

Search and delete these files

[ Learn More ]
There may be some component 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.
%User Temp%\csrss{number}.dll
%System%\csrss{number}.dll
%System Root%\Documents and Settings\All Users\Application Data\loggy.txt

Step 6

Scan your computer with your Trend Micro product to delete files detected as BKDR_BANDOK.SM. 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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