1. Symantec/
  2. Security Response/
  3. Trojan.Farfli


Risk Level 1: Very Low

July 29, 2007
July 29, 2007 8:51:54 AM
Also Known As:
Infection Length:
Systems Affected:
The Trojan may be downloaded from one of the following remote locations:
  • [http://]install1.ring520.org/kk[REMOVED]
  • [http://]install2.ring520.org/kk[REMOVED]
  • [http://]install3.ring520.org/kk[REMOVED]
  • [http://]install4.ring520.org/kk[REMOVED]

Once the downloaded file is executed, it drops the following files:
  • %System%\[RANDOM 8 CHARACTER NAME].dll
  • %System%\drivers\[RANDOM 1].sys
  • %System%\drivers\[RANDOM 2].sys
  • %System%\[RANDOM].exe

It then creates following file:
%UserProfile%\Favorites\[CHINESE CHARACTERS].url

It adds the following URL as a bookmark in Internet Explorer:

Next, the Trojan creates following registry subkeys:
  • HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\[RANDOM 1]
  • HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\[RANDOM 2]
  • HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Control\Class\{8ECC055D-047F-11D1-A537-0000F8753ED1}
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\[RANDOM 1]
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\[RANDOM 2]

Note: [RANDOM 1] and [RANDOM 2] are random values that match the dropped file names. [RANDOM] is just a random value.

It then attempts to download a file from the following URL:

It notifies the remote attacker that the computer has been infected by accessing the following URL:

The Trojan then checks the hosts file to see if the file contains the following strings:
  • 9991
  • 2345
  • 7322
  • 7255
  • 6781

It modifies the hosts file to the following: localhost

The Trojan also modifies the start page of Internet Explorer to one of following URLs:
  • [http://]www.baidu.com/inde[REMOVED]
  • [http://]www.kzdh.com[REMOVED]
  • www.7255.com/?g
  • about.blank.la?g

It thenhooks or patches ZwSetValueKey to prevent other threats or security risks overwriting the Start Page registry entry.

If it finds a specific Web browser installed, it modifies the following .ini file so that when a user performs a search it is conducted via the Baidu URL with the specific affiliate name:
Maxthon Browser .ini file: [MAXTHON INSTALLATION FOLDER]\Config\setupcenter.ini
TheWorld Browser .ini file: [THEWORLD INSTALLATION FOLDER]\TheWorld.ini

The modified URL is the following:


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.
Writeup By: Kaoru Hayashi
Summary| Technical Details| Removal

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