W95.Hybris.gen

When the worm attachment is executed, the Wsock32.dll file is modified or replaced. Once the worm has infected wsock32.dll, it has the ability to monitor the Internet connection as well as incoming and outgoing email traffic. The worm then scans for email addresses. When an email address is detected whether on an Internet site or in email being sent or received, the worm waits for a period of time and then sends an infected message to the detected address.

The worm attempts to connect to the alt.comp.virus newsgroup. If it connects successfully, then the worm uploads its own plug-ins to this newsgroup in an encrypted form. It goes thru the subject header of the messages, and tries to match a specific format. The subject header will also specify the version number of the attached plug-in if the plug-ins are present. If newer versions of the plug-ins are found, the worm downloads them and updates its behavior.

One of the plug-ins for W95.Hybris.gen generates a spiral image. Upon execution, the plug-in initially loads OpenGL libraries which are used to draw a large black and white spiral image. It also registers itself as a service; this prevents it from being displayed in the Close Programs dialog box. For additional information on this, see the document W95.Hybris.Plugin.

This worm also has a plug-in that infects executable programs. The DOS EXE infection is fairly simple dropping technique. The virus code is appended to the end of the file with a small 16-bit dropper routine. This routine creates a temporary file with an .exe extension in the TEMP folder and executes it. It then deletes the temporary executable. In this way, Wsock32.dll is infected with the actual worm body. The PE executables have a much more complicated file infection process. PE files become infected only if they have a long enough code section. The virus infection plug-in packs the original code area and overwrites it if it will fit in the same place. This complicated antiheuristic infection technique is difficult but possible to repair.

If Wsock32.dll is being used by the system, the worm cannot modify it. In this situation, the worm will add a registry entry to one of the following subkeys:

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\RunOnce

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce

It always alternates between these two keys as the worm spreads from one computer to another. The worm hooks onto the following exports of Wsock32.dll:

send()
recv()
connect()

Whenever you send email, the worm sends a second message to the same person, attaching a copy of itself using a randomly generated file name.

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.

Summary