W32.Mumu.B.Worm

SUMMARY

W32.Mumu.B.Worm is a worm that spreads through network shares. The main worm component is a file named Mumu.exe. The worm will create various files on the infected system, including both legitimate utilities and malicious files. Symantec products will detect the malicious files as Trojan.Mumuboy and Hacktool.Hacline.

Protection

• Virus Definitions (LiveUpdate™ Weekly) June 26, 2003
• Virus Definitions (Intelligent Updater) June 26, 2003

Threat Assessment

Wild

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

Damage

• Damage Level: Medium
• Degrades Performance: Network copying may cause performance degradation.

Distribution

• Distribution Level: Medium
• Ports: 139
• Shared Drives: Copies across remotely accessible shares.

TECHNICAL DETAILS

W32.Mumu.B.Worm includes several components that provide the worm with specific functionality. The worm synchronously drops and runs the components. The worm also parses the results of their execution.

The following illustration represents W32.Mumu.B.Worm and the components carried in its resources:





When W32.Mumu.B.Worm is run, it performs the following actions:

1. Creates one of the following two mutexes:
   • aQjinfo1mutex
   • aQjinfo2mutex
     
     
2. Locates and drops the following files from its resources:
   • %System%Kavfind.exe (30,208 bytes; detected as Hacktool.Hacline)
   • %System%Last.exe (20,480 bytes; detected as Trojan.Mumuboy)
   • %System%Psexec.exe (36,352 bytes; legitimate Remote Process Launcher application by SysInternals)
   • %System%IPcpass.txt (510 bytes; list of passwords that Hacktool.Hacline uses)
     
     Note: %System% is a variable. The worm locates the System folder and copies itself to that location. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
     
     
3. Launches Last.exe (Trojan.Mumuboy).
   
   
4. Copies itself to %System%Mumu.exe.
   
   
5. Creates the following registry to mark its presence:
   
   HKEY_LOCAL_MACHINESOFTWAREmumu
   
   
6. Synchronously launches Hacktool.Hacline, with the supplied IP address range of targets. When run, Hacktool.Hacline performs the following actions:
   
   Checks for a presence of the file, IPCpass.txt, which W32.Mumu.B.Worm dropped. This file contains names/passwords for the dictionary attack. If this file is not found, Hacktool.Hacline will use an internal hard-coded list of names and passwords.
   
   Attempts to establish a socket connection with the target via port 139/TCP (NetBIOS Session Service) to check whether the target runs the SMB service over TCP/IP.
   
   If port 139/TCP is available, Hacktool.Hacline will attempt to establish a Null Session connection (Anonymous Logon connection) with the \%target_IP%IPC$.
   
   NOTE: %target_IP% is an IP address enumerated within the supplied IP address range of targets. Hacktool.Hacline uses the Anonymous Null Session Passwords Exploit on the target system to obtain the list of users (CVE-2000-1200). This functionality might have derived from W32.HLLW.Lioten.
   
   Once a Null Session connection is established, Hacktool.Hacline will enumerate all the user accounts on the target system (all types of accounts).
   
   Any enumerated user accounts are added to the dictionary.
   
   Finally, Hacktool.Hacline launches a weak password dictionary attack to establish a connection with the share \%target_IP%Admin$.
   Dictionary entries may be used as both usernames and the passwords. Details of every successfully established connection are logged in the IPCfind.txt file.
   
   NOTE: Hacktool.Hacline launches multiple threads with repeated login attempts, which may result in possible locked out accounts.
   
   As soon as Hacktool.Hacline quits, the worm inspects the IPCfind.txt file. For every connectable SMB share, it will attempt to establish connection using a legitimate tool, Net.exe. Then, the worm will attempt to copy itself into the target system as \%target_IP%admin$system32mumu.exe.
   
   Then, W32.Mumu.B.Worm launches the Remote Process application to start the remote file, %System%Mumu.exe.
   
   The IP ranges specified for the Hacktool.Hacline depend on the local host IP address, or they are randomly generated. Also, the worm will run Netstat.exe to inspect any currently established connections. For every "pingable" IP address with which the local host has an open connection, Hacktool.Hacline will be launched to reveal whether the network resource can be compromised.
   
   
7. When W32.Mumu.B.Worm runs the Trojan.Mumuboy executable, it performs the following actions:
   • Creates the mutex, aQjaashyuhv1_0, to ensure that only one instance runs.
   • Drops itself as %Windir%Bboy.exe.
   • Creates the value:
     
     "Kernel"="%Windir%boy.exe"
     
     in the registry key:
     
     HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
     
     
   • Drops the file, Bboy.dll (36,864 bytes), into the %System% folder. This file is also detected as Trojan.Mumuboy.
   • Attempts to terminate the following processes:
     • pfw.exe
     • Iparmor.exe
     • Eghost.exe
     • PasswordGuard.exe
     • Dfvsnet.exe
     • Kvfw.exe
     • kvapfw.exe
       
       
   • Installs a hook into the hook chain to intercept any keystrokes, including passwords, login details, and so on.
   • Logs intercepted data in the file, Qjinfo.ini.
   • Emails the file, Qjinfo.ini, using a separate thread via the HTTP mail server, www.58589.com. The email contains the following characteristics:
     From: babyj@8848.com
     To: <email address that is specified at the offset 0x40 in the Trojan.Mumuboy executable file> (for example, terminal2000@163.com)
     BCC: cq@58589.com
     
     
8. W32.Mumu.B.Worm expects that Trojan.Mumuboy logs intercepted data in the file, Qjinfo.ini. Therefore, it waits for 2.5 minutes, and then sends this file by email again. This time, an internal SMTP client engine is used. The submitted email is sent via the smtp.sina.com.cn SMTP server.
   It has the following characteristics:
   
   From: reint0.student@sina.com
   To: sendmail2.student@sina.com
   Subject: <current day of month>
   Attachment: Qjinfo.ini (contains intercepted data)
   
   
9. Attempts to register itself by creating the value:
   
   "Folder Service"="qjinfo.exe"
   
   in the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   However, it appears that the file, Qjinfo.exe, is not dropped

NOTE: The file, Qjinfo.exe, has been received in a number of separate submissions. We assume that Qjinfo.exe represents an earlier version of W32.Mumu.B.Worm, due to the following reasons:

• It has been compiled earlier.
• Its functionality is a subset of the current version of W32.Mumu.B.Worm.

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

Removal using the W32.Mumu.B.Worm Removal Tool
Symantec Security Response has created a tool to remove W32.Mumu.B.Worm, which is the easiest way to remove this threat.

Manual Removal
As an alternative to using the removal tool, you can manually remove this threat.


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

1. Disable System Restore (Windows Me/XP).
2. Finding and stopping the Mumu.exe and Last.exe processes.
3. Update the virus definitions.
4. Run a full system scan and delete all the files detected as W32.Mumu.B.Worm, Hacktool.Hacline, or Trojan.Mumuboy.
5. Reverse the changes that the worm made to the registry.

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

1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:

• "How to disable or enable Windows Me System Restore"
• "How to turn off or turn on Windows XP System Restore"

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.

2. Finding and stopping the Mumu.exe and Last.exe processes

1. Press Ctrl+Alt+Delete once.
2. Click Task Manager.
3. Click the Processes tab.
4. Double-click the Image Name column header to alphabetically sort the processes.
5. Scroll through the list and look for Mumu.exe and Last.exe.
6. As you find each process, click it, and then click End Process.
7. Exit the Task Manager.

3. 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: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

4. 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.Mumu.B.Worm, Hacktool.Hacline, or Trojan.Mumuboy, click Delete.

5. Reversing the changes made to the registry

CAUTION: Symantec strongly recommends that you back up the registry before making 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 values:
   
   Kernel
   
   and:
   
   Folder Service
   
   
5. Exit the Registry Editor.
   
   
6. Delete the log file qjinfo.ini.