1. Symantec/
  2. Security Response/
  3. Backdoor.Ryknos.B


Risk Level 2: Low

November 10, 2005
February 13, 2007 12:46:22 PM
Also Known As:
Troj/Stinx-F [Sophos], BKDR_BREPLIBOT.D [Trend Micro], Breplibot.C [F-Secure], Win32.OutsBot.V [Computer Asso
Trojan Horse
Systems Affected:

When Backdoor.Ryknos.B is executed, it performs the following actions:
  1. Copies itself as %System%\$sys$xp.exe.

    Note: %System% is a variable that refers to the System folder. By default this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

  2. Uses the XCP software to hide the copy of the Trojan file and the registry subkey it creates, if the XCP software is installed after the Trojan. The Trojan will not be installed if the compromised computer has the XCP software present, which is itself installed when inserting certain Sony BMG content-protected music CDs.

  3. Creates one of the following mutexes, so that only one instance of it runs on a compromised computer at any one time:

    • Super
    • $sys$xp.exe

  4. Adds the value:

    "$sys$cmp" = "$sys$xp.exe"

    to the registry subkey:


    so that it runs every time Windows starts.

  5. Attempts to send a notification message to a predetermined IP address, using TCP port 8080.

  6. Attempts to add itself as a trusted application to the Windows Firewall.

  7. Provides back door capabilities by connecting to one of the following IRC servers, joining to an IRC channel and listening for commands:


  8. Allows a remote attacker to perform any of the following actions:

    • Send sensitive information, such as the host and user name, operating system version, and IP address
    • Download and execute remote files


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: Yana Liu
Summary| Technical Details| Removal

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