1. Symantec/
  2. Security Response/
  3. Downloader.Nflog


Risk Level 1: Very Low

December 5, 2012
December 20, 2012 11:40:46 AM
Infection Length:
Systems Affected:
When the Trojan is executed, it registers itself as the following service:
Description: IPv6 Stack Local Support
ImagePath: %SystemDrive%\System32\svchost.exe -k netsvcs
Startup type: Automatic

It creates the following registry subkey in order to register the above service:

Next it checks for Internet connectivity by attempts to connect to the following location:

If the connection fails, it attempts to modify proxy settings in the following registry subkey in order to establish a connection:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Micorsoft\Windows\CurrentVersion\Internet Settings\ProxySettingsPerUser

Once Internet connectivity has been established, the Trojan downloads the following executable file:

Next, the Trojan creates the following registry entry as an infection marker:

The Trojan then collects the following system information and sends it to a remote command-and-control (C&C) server:
  • A list of recently accessed files
  • A list of running processes
  • A list of running services
  • Available network shares
  • Established connections and ports
  • Hardware information, including: bios, network cards etc.
  • Network adapter information
  • Operating system information, including: version, product ID, registered owner etc.

Next, the Trojan may download more malware on to the compromised computer. It has been observed to download Backdoor.Nflog and Trojan.Taidoor.


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: Alan Neville
Summary| Technical Details| Removal

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