Backdoor.Berbew

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Discovered: July 16, 2003
Updated: February 13, 2007 12:03:53 PM
Also Known As: Troj/Webber-A [Sophos], BackDoor-AXJ [McAfee], TrojanProxy.Win32.Webber.10 [K, Win32.Webber [Computer Associa, BKDR_WEBBER.A [Trend]
Type: Trojan Horse
Systems Affected: Windows


Backdoor.Berbew is a Backdoor Trojan Horse that is downloaded from the Internet by Trojan.Download.Berbew. The Backdoor Trojan steals passwords and delivers them in the form of URL requests to the Web site of the Trojan's creator. Port numbers 7714 and 8546 may be opened for listening (the port numbers may vary).

Antivirus Protection Dates

  • Initial Rapid Release version July 16, 2003
  • Latest Rapid Release version July 08, 2019 revision 006
  • Initial Daily Certified version July 16, 2003
  • Latest Daily Certified version July 08, 2019 revision 020
  • Initial Weekly Certified release date July 16, 2003

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.


Technical Description


Symantec Security Response received a number of submissions in the form of the following email message:

From (spoofed): Citibank Accounting <accounting@web.da.us.citibank.com>
Subject : Re: Your credit application
Message Body :
Dear sir,
Thank you for your online application for a Citibank Home Equity Loan. In order to be approved for any loan application we pull your Credit Profile and Chexsystems information, which didn't satisfy our minimum needs. Consequently, we regret to say that we cannot approve you for Citibank Home Equity Loan at this time.
*Attached are copy of your Credit Profile and Your Application that you submitted with us.
Please take a close look at it, you will receive hard copy by mail withing next few days.

Attachment : web.da.us.citi.heloc.pif (5,664 bytes)

The attachment is Trojan.Download.Berbew. When it is run, it downloads Backdoor.Berbew (39,140 bytes) from the Internet and saves it into the %System% folder as Rtdx32.exe and then runs it.

When Backdoor.Berbew runs, it performs the following actions:

  1. Creates the mutex "Webber10_" to make sure it runs in a single instance.

  2. Drops itself as %System%\<random filename>.exe. The <random filename> consists of eight random letters. It may also consist of six random letters with the string "32" appended. The first letter is a capital.

    For example, it may drop itself as %System%\Gmhhoj32.exe or %System%\Djbpnoof.exe.

  3. Drops the file, %System% <random filename>.dll. The <random filename> is generated by the same rules as the dropper's name. The size of the .dll file is 5,633 bytes, and Symantec products detect it as Backdoor.Berbew. Backdoor.Berbew uses the .dll file to launch the Backdoor.Berbew executable.

  4. Creates the registry key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\
    {79FA9088-19CE-715D-D85A-216290C5B738}\InProcServer32

    so that the Trojan runs when you start Windows.

  5. Creates the (Default) value in the aforementioned registry key and sets to the dropped .dll filename.

    For example, the Trojan may set the default value to %System%\Oikenhgi.dll.

  6. Creates the value:

    "ThreadingModel"="Apartment"

    in the aforementioned registry key.

  7. Creates the value:

    "Web Event Logger"="{79FA9088-19CE-715D-D85A-216290C5B738}"

    in the registry key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\
    ShellServiceObjectDelayLoad

    so that the .dll file is loaded when you start Windows. Backdoor.Berbew patches the contents of the dropped .dll file by writing its own filename into it so that the .dll file knows the name of the Backdoor.Berbew executable file and can then run it.

  8. Reads data that is appended to it, decrypts it, and uses it as its own configuration data. The configuration data may include the port numbers that the backdoor uses, the URL to other configuration files, the URL to submit the system information and intercepted data, and so on.

  9. Attempts to obtain an access to the password cache that is stored on the local computer. The cached passwords include modem and dial-up passwords, URL passwords, share passwords, and others.

    The Trojan may use the following files to log the passwords and to store downloaded configuration data:
    • %System%\NtXgl16.dat
    • %System%\NtXgl16.vxd
    • %System%\NtXgl16.sys

  10. Enumerates active windows and attempts to intercept any entered data. Also, it intercepts the contents of the clipboard. The Trojan may also target Internet bank accounts to steal login details.

    To effectively intercept entered data, the Trojan wants a user to specifically enter the login details. For this purpose, it attempts to disable password caching and to disallow Autocomplete, by setting the following registry values:

    "FormSuggest Passwords"="yes"
    "FormSuggest PW Ask"="yes"
    "Use FormSuggest"="yes"

    in the registry key:

    HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main

  11. Opens ports that are specified in its appended configuration data and listens on them for incoming connections. The port numbers may vary. The sample available at the time of the Backdoor.Berbew analysis contained the port numbers 7714 and 8546.


Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.


Removal


The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Restart your computer in Safe mode or VGA mode.
  2. Update the virus definitions.
  3. Run a full system scan and delete all the files detected as Backdoor.Berbew or Trojan.Download.Berbew.
  4. Delete the registry key and the value that were added to the registry.

For specific details on each of these steps, read the following instructions.

1.
Restarting the computer in Safe mode or VGA mode
  • For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions on restarting in Safe mode, refer to the document, "How to start the computer in Safe Mode."
  • For Windows NT 4 users, restart the computer in VGA mode.

NOTE: If Norton AntiVirus reports that it cannot delete an infected file, shut down the computer, turn off the power, and wait 30 seconds. Restart the computer in Safe mode (Windows 95/98/Me/2000/XP) or VGA mode (Windows NT 4) and run the scan again.

2. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).

    The
    Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.
3. Scanning for and deleting the infected files
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with Backdoor.Berbew or Trojan.Download.Berbew, click Delete.

4. Deleting the registry key and the value from the registry


CAUTION : Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry ," for instructions.
  1. Click Start, and then click Run. (The Run dialog box appears.)
  2. Type regedit

    Then click OK. (The Registry Editor opens.)
  3. Navigate to and delete the key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\
    {79FA9088-19CE-715D-D85A-216290C5B738}\InProcServer32
  4. Navigate to the key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\
    ShellServiceObjectDelayLoad
  5. In the right pane, delete the value:

    "Web Event Logger"="{79FA9088-19CE-715D-D85A-216290C5B738}"
  6. Exit the Registry Editor.

Writeup By: Sergei Shevchenko