Analysis by: Sabrina Lei Sioting
ALIASES:

Backdoor.Cycbot!gen3 (Symantec); Backdoor:Win32/Cycbot.B (Microsoft); Backdoor.Win32.Gbot.acf (Kaspersky); BackDoor-EXI.gen.i (Mcafee)

 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

This backdoor opens a random port to allow a remote user to connect to the affected system. Once a successful connection is established, the remote user executes commands on the affected system.

  TECHNICAL DETAILS

Ports: Random
File Size: 209,408 bytes
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 14 Mar 2011

Installation

This backdoor drops the following copies of itself into the affected system:

  • %User Profile%\Application Data\dwm.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

It drops the following files:

  • %User Profile%\Application Data\9EAE.6BA

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "explorer.exe,%User Profile%\Application Data\dwm.exe"

Other System Modifications

This backdoor modifies the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings
ProxyEnable = "1"

(Note: The default value data of the said registry entry is 0.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Hardware Profiles\0001\Software\
Microsoft\windows\CurrentVersion\
Internet Settings
ProxyEnable = "1"

(Note: The default value data of the said registry entry is 0.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Hardware Profiles\Current\Software\
Microsoft\windows\CurrentVersion\
Internet Settings
ProxyEnable = "1"

(Note: The default value data of the said registry entry is 0.)

HKEY_CURRENT_CONFIG\Software\Microsoft\
windows\CurrentVersion\Internet Settings
ProxyEnable = "1"

(Note: The default value data of the said registry entry is 0.)

Backdoor Routine

This backdoor opens a random port to allow a remote user to connect to the affected system. Once a successful connection is established, the remote user executes commands on the affected system.

  SOLUTION

Minimum Scan Engine: 8.900

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_CYCBOT.QS

[ 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 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 NT\CurrentVersion\Winlogon
    • Shell = "explorer.exe,%User Profile%\Application Data\dwm.exe"

Step 4

Restore this modified 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\Internet Settings
    • From: ProxyEnable = "1"
      To: ProxyEnable = "0"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware Profiles\0001\Software\Microsoft\windows\CurrentVersion\Internet Settings
    • From: ProxyEnable = "1"
      To: ProxyEnable = "0"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware Profiles\Current\Software\Microsoft\windows\CurrentVersion\Internet Settings
    • From: ProxyEnable = "1"
      To: ProxyEnable = "0"
  • In HKEY_CURRENT_CONFIG\Software\Microsoft\windows\CurrentVersion\Internet Settings
    • From: ProxyEnable = "1"
      To: ProxyEnable = "0"

Step 5

Search and delete this file

[ 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 Profile%\Application Data\9EAE.6BA

Step 6

Scan your computer with your Trend Micro product to delete files detected as BKDR_CYCBOT.QS. 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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