W32.HLLW.Deloder

SUMMARY

While Symantec Security Response is seeing an increase in submissions of W32.HLLW.Deloder, Symantec DeepSight Threat Management System has shown an overall decrease in activity on port 445. Security Response will continue to monitor this threat, and take action as appropriate.

W32.HLLW.Deloder is a network-aware worm that attempts to connect to a target host, using TCP port 445. This worm affects Windows 2000 and Windows XP only.

If the worm makes a successful connection, it copies the file, Inst.exe, to locations that are hard-coded in the worm. Inst.exe is a backdoor Trojan component that is detected as Backdoor.Dvldr. Then, W32.HLLW.Deloder will load from the Startup folder when you start Windows.

W32.HLLW.Deloder attempts to launch several remote services, which:

• Copies and executes the backdoor Trojan
• Copies and executes the worm
• Deletes the default shares
• Changes the attributes of the worm and backdoor Trojan to Read only

The worm exists as the Dvldr32.exe file and is packed with ASPack.

Protection

• Virus Definitions (LiveUpdate™ Weekly) March 9, 2003
• Virus Definitions (Intelligent Updater) March 9, 2003

Threat Assessment

Wild

• Wild Level: Medium
• Number of Infections: 50 - 999
• Number of Sites: More than 10
• Geographical Distribution: Medium
• Threat Containment: Easy
• Removal: Moderate

Damage

• Damage Level: Medium
• Degrades Performance: Increased activity on TCP port 445
• Causes System Instability: Deletes default shares

Distribution

• Distribution Level: Medium
• Ports: 445
• Shared Drives: Copies itself across shares to which it can connect using a set of default passwords

TECHNICAL DETAILS

When W32.HLLW.Deloder is run, it does the following:

1. Creates the mutex, testXserv.
   
2. Creates the value:
   
   messnger   [worm filename]
   
   in the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   so that the worm runs when you start Windows.
   
3. Copies the following two files, which are carried in the worms resources, to your computer:
   • Psexec.exe: This file is 36,352 bytes and is a legitimate remote process launcher. This file is not malicious. The worm uses it to replicate itself.
   • Inst.exe: This file is 684,562 bytes and is an installer of the Trojan, Backdoor.Dvldr, and is detected as such.
     
     
4. Launches multiple network replication threads. Every thread generates a random IP address. For every address, the worm attempts to:
   • Establish a connection using TCP port 445.
   • Copy the dropped Backdoor.Dvldr installer to the remote unrestricted share as the following files:
     • <random_ip>C$Documents and SettingsAll UsersStart MenuProgramsStartupinst.exe
     • <random_ip>CWINDOWSStart MenuProgramsStartupinst.exe
     • <random_ip>C$Documents and SettingsAll UsersStart MenuProgramsStartupinst.exe
       
       
5. Inventories network resources and attempts to make a connection to each of them. If the shared resource is password-protected, then the worm attempts to connect to it using a brute-force attack. The worm uses an internal hard-coded list of various passwords that might have been used to restrict the shares, such as "admin," "pass," "12345," and so on.
   
6. Attempts to copy and run both itself and Backdoor.Dvldr, by using the legitimate remote process launcher.
   
7. Attempts to delete the following default shares (This action is not considered permanent, as the shares will be restored when you restart the computer):
   • E$
   • IPC$
   • ADMIN$
   • F$
   • D$
   • C$

Symantec ManHunt
To specifically detect this threat as W32.HLLW.Deloder, Symantec recommends that users of the Symantec ManHunt product activate the HYBRID MODE function and apply the following custom rule:

*******************start file********************

alert tcp any any -> any any (msg:"W32.HLLW.Deloder infection"; content: "|59 49 39 E0 C3 1D D3 4D D8 F2 61 73 73 6B 47 69 DA B5 BC 05 3A F0 E4 C7 98 76 CB B4 37 A4 39 4A|";)

*************EOF*********************

This rule will trigger on successful penetration attacks made by the worm. Please note that this signature was not designed to detect unsuccessful attacks made by the worm.

For more information on how to create custom signatures, refer to the "Symantec ManHunt Administrative Guide: Appendix A Custom Signatures for HYBRID Mode."

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

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions.
2. Run a full system scan and delete all the files detected as W32.HLLW.Deloder or Backdoor.Dvldr.
3. Delete the value that was added to the registry.
   

For specific details on each of these steps, read the following instructions.

1. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
• Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).
  
  The Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

2. Scanning for and deleting the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec Corporate antivirus product is set to scan All Files."
2. Run a full system scan.
3. If any files are detected as infected with W32.HLLW.Deloder or Backdoor.Dvldr, click Delete.

3. Deleting the value from the registry

CAUTION: Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry," for instructions.

1. Click Start, and then click Run. (The Run dialog box appears.)
2. Type regedit
   
   Then click OK. (The Registry Editor opens.)
   
3. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, delete the value:
   
   messnger   [worm filename]
   
5. Exit the Registry Editor.