W32.Chainsaw.Worm

SUMMARY

W32.Chainsaw is a network worm. It spreads to shared drives as Chainsaw.exe. The file has the hidden attribute.

Protection

• Virus Definitions (Intelligent Updater) September 14, 2000

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Medium
• Payload Trigger: 31st Day of the Month, Random
• Degrades Performance: Starts DoS attacks against a random IP
• Causes System Instability: Random counter may create a Trojan that erases hard drive

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

If Chainsaw.exe is run, it creates the Winmine.exe file in the Windows folder. It also creates the value:

Mines

in the registry key

HKEY_CURRENT_USERSoftwareMicrosoft
WindowsCurrentVersionRun

The first time that the worm is run, it disables the ZoneAlarm firewall program if it is installed. It also posts the following message to the alt.horror newsgroup:

From: Leatherface
Subject: CHAINSAWED
Message: WHO WILL SURVIVE AND WHAT WILL BE LEFT OF THEM?

W32.Chainsaw spreads by randomly picking IP addresses and testing to see if they are infected with SubSeven or NetBus, or if they use NetBIOS. If the test is successful, it uses the backdoor to install and run itself.

The worm also has a random counter that, when triggered, creates a Trojan program. The Trojan overwrites the hard disk with the following text:

THE FILM WHICH YOU ARE ABOUT TO SEE IS AN ACCOUNT OF THE TRAGEDY WHICH BEFELL A GROUP OF FIVE YOUTHS. IN PARTICULAR SALLY HARDESTY AND HER INVALID BROTHER FRANKLIN. IT IS ALL THE MORE TRAGIC IN THAT THEY WERE YOUNG. BUT, HAD THEY LIVED VERY, VERY LONG LIVES, THEY COULD NOT HAVE EXPECTED NOR WOULD THEY HAVE WISHED TO SEE AS MUCH OF THE MAD AND MACABRE AS THEY WERE TO SEE THAT DAY. FOR THEM AN IDYLLIC SUMMER AFTERNOON DRIVE BECAME A NIGHTMARE. THE EVENTS OF THAT DAY WERE TO LEAD TO THE DISCOVERY OF ONE OF THE MOST BIZARRE CRIMES IN THE ANNALS OF AMERICAN HISTORY, THE TEXAS CHAIN SAW MASSACRE...

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. 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.

REMOVAL

To remove this worm:

• Delete Chainsaw.exe and Winmine.exe (restoration of Winmine is optional).
• Remove the Mines value from the Run key.
• Scan with NAV and check for the SubSeven and NetBus Backdoor Trojans.

To delete the worm files:

1. Click Start, point to Find (or Search), and then click Files or Folders.
2. Make sure that Look in is set to (C:) and that Include subfolders is checked.
3. In the Named box, type--or copy and paste--the following file names:
   
   chainsaw.exe winmine.exe
   
4. Click Find Now.
5. Delete the files that are found.

NOTE: The Winmine.exe file is a Windows game. Reinstallation is optional.

To edit the registry:

CAUTION: We strongly recommend that you back up the system registry before you make any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Please make sure that you modify only the keys that are specified. Please see the document How to back up the Windows registry before you proceed.

1. Click Start, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to the following subkey:
   
   HKEY_CURRENT_USERSoftwareMicrosoft
   WindowsCurrentVersionRun
   
4. In the right pane, locate and delete the value:
   
   Mines
   
5. Close the Registry Editor.

To scan with Norton AntiVirus:

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start Norton AntiVirus (NAV), and run a full system scan, making sure that NAV is configured to scan all files.
3. Delete any files that are detected as SubSeven or NetBus.