1. Symantec/
  2. Security Response/
  3. W32.Opaserv.J.Worm

W32.Opaserv.J.Worm

Risk Level 2: Low

Discovered:
December 20, 2002
Updated:
February 13, 2007 11:56:26 AM
Type:
Worm
Systems Affected:
Windows
CVE References:
CVE-2000-0979

When the W32.Opaserv.J.Worm runs on Windows 95-/98-/Me-based computers, it does the following:

It checks for the value

Srv32Old

in the registry key

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices

If the value exists, the worm deletes the file to which the Srv32Old value points.

If the the Srv32Old value does not exist, then the worm determines whether the value

Srv32

exists in the registry key

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices

If the value does not exist, the worm adds the value

Srv32        C:\WINDOWS\Srv32.exe

to that registry key.

Next, the worm checks whether it is being run as the file C:\Windows\Srv32.exe. If it is not, the worm copies itself as this file name and adds the value

Srv32Old   <Path\original worm name>

to the registry key

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices

After the worm checks the registry values and the location from where it is executing, the worm checks to make sure that only one instance of the worm is running in memory. It does this by creating a mutex that has the name Srv3231415.

The worm registers itself as a process if it is not already executing.

Then, the worm takes inventory of the network looking for "C:\" shares. For each share that it finds, it copies itself to C:\Windows\svr32.exe.

The worm uses a security vulnerability in Microsoft Windows 95/98/Me. It sends single-character passwords to network shares to get access to Windows 95/98/Me file shares, without knowing the entire password assigned to the shares. The affected operating systems include:
  • Microsoft Windows 95
  • Microsoft Windows 98
  • Microsoft Windows 98 Second Edition
  • Microsoft Windows Me

A patch for computers that run these operating systems can be found at http://www.microsoft.com/technet/security/bulletin/MS00-072.asp.

The worm is apparently coded to add the following line to the Win.ini file:

run=c:\windows\src32.exe

However, in actual infections or detections, the worm does not add this line to the file Win.ini.
    The worm appears to be able to update itself by reading files from a Web site whose URL is hard-coded into the worm. The worm attempts to download an update named Sccss.

    The W32.Opaserv.J.Worm also has Backdoor capabilities, which give an attacker unauthorized access to a compromised computer. The worm opens a randomly chosen TCP port and UDP port to connect to the attacker.

    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.
    Writeup By: Yana Liu
    Summary| Technical Details| Removal

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