W32.Mytob.F@mm

SUMMARY

W32.Mytob.F@mm is a mass-mailing worm that uses it own SMTP engine to send an email to addresses that it gathers from the Windows Address Book on the compromised computer. The email has a variable subject and attachment name.

The worm also has the ability to open a back door and spread through the network by exploiting the Microsoft Windows Local Security Authority Service Remote Buffer Overflow (described in Microsoft Security Bulletin MS04-011).

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (LiveUpdate™ Weekly) March 16, 2005
• Virus Definitions (Intelligent Updater) March 15, 2005

Threat Assessment

Wild

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

Damage

• Damage Level: Medium
• Payload: Opens a back door.
• Large Scale E-mailing: Sends an email to addresses gathered from the compromised computer.
• Compromises Security Settings: Blocks access to security-related Web sites.

Distribution

• Distribution Level: High
• Subject of Email: Varies
• Name of Attachment: Varies with a .bat, .cmd, .exe, .pif, .scr, or .zip file extension.
• Ports: TCP port 8080.

TECHNICAL DETAILS

When W32.Mytob.E@mm is executed, it performs the following actions:

1. Creates the following copies of itself:
   
   
   • %System% askgmr.exe
   • %System%winnett.exe
     
     Note: %System% is a variable that refers to the System folder. By default this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
     
     
2. Adds the value:
   
   "SVCHOST" = "taskgmr.exe"
   
   to the registry subkeys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersion
   RunServices
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_CURRENT_USERSoftwareMicrosoftOLE
   HKEY_CURRENT_USERSYSTEMCurrentControlSetControlLsa
   HKEY_LOCAL_MACHINESoftwareMicrosoftOLE
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlLsa
   
   so that it runs every time Windows starts.
   
   
3. Gathers email addresses from the Windows Address Book and from files with the following extensions:
   
   
   • .wab
   • .adb
   • .tbb
   • .dbx
   • .asp
   • .php
   • .sht
   • .htm
   • .pl
     
     The worm will ignore email addresses that contain any of the following strings:
     
     
   • -._!
   • -._!@
   • .edu
   • .gov
   • .mil
   • abuse
   • accoun
   • acketst
   • admin
   • anyone
   • arin.
   • avp
   • be_loyal:
   • berkeley
   • borlan
   • bsd
   • bugs
   • ca
   • certific
   • contact
   • example
   • spam
   • feste
   • fido
   • foo.
   • fsf.
   • gnu
   • gold-certs
   • google
   • gov.
   • help
   • hotmail
   • iana
   • ibm.com
   • icrosof
   • icrosoft
   • ietf
   • info
   • inpris
   • isc.o
   • isi.e
   • kernel
   • linux
   • listserv
   • math
   • me
   • mit.e
   • mozilla
   • msn.
   • mydomai
   • no
   • nobody
   • nodomai
   • noone
   • not
   • nothing
   • ntivi
   • page
   • panda
   • pgp
   • postmaster
   • privacy
   • rating
   • rfc-ed
   • ripe.
   • root
   • ruslis
   • samples
   • secur
   • sendmail
   • service
   • site
   • soft
   • somebody
   • someone
   • sopho
   • spm
   • submit
   • support
   • syma
   • tanford.e
   • the.bat
   • unix
   • usenet
   • utgers.ed
   • webmaster
   • www
   • you
   • your
     
     The worm may also add one of the following names to domain names gathered from the compromised computer to generate email addresses:
     
     
   • adam
   • alex
   • alice
   • andrew
   • anna
   • bill
   • bob
   • brenda
   • brent
   • brian
   • claudia
   • dan
   • dave
   • david
   • debby
   • fred
   • george
   • helen
   • jack
   • james
   • jane
   • jerry
   • jim
   • jimmy
   • joe
   • john
   • jose
   • julie
   • kevin
   • leo
   • linda
   • maria
   • mary
   • matt
   • michael
   • mike
   • peter
   • ray
   • robert
   • sam
   • sandra
   • serg
   • smith
   • stan
   • steve
   • ted
   • tom
     
     
4. Appends the following prefixes to domain names in an attempt to find Simple Mail Transfer Protocol (SMTP) servers:
   
   
   • gate.
   • ns.
   • relay.
   • mail1.
   • mxs.
   • mx1.
   • smtp.
   • mail.
   • mx.
     
     
5. Uses its own SMTP engine to send itself to the email addresses that it finds. The email has the following characteristics:
   
   From: Spoofed
   
   Subject:
   One of the following:
   
   
   • hello
   • God day
   • Error
   • Status
   • Mail Transaction Failed
   • Mail Delivery System
   • Server Report
   • (No Subject)
   • (random letters)
     
     Message:
     One of the following:
     
     
   • The message cannot be represented in 7-bit ASCII encoding and has been sent as a binary attachment.
   • Mail transaction failed. Partial message is available.
   • The message contains Unicode characters and has been sent as a binary attachment.
   • The original message was included as an attachment.
   • Here are your banks documents.
   • The original message was included as an attachment.
   • (No body)
   • (Random data)
     
     Attachment:
     The attachment may contain one of the following file names:
     
     
   • body
   • data
   • doc
   • document
   • file
   • message
   • readme
   • test
   • text
   • (random letters)
     
     with one of the following extensions:
     
     
   • .bat
   • .cmd
   • .exe
   • .pif
   • .scr
   • .zip
     
     If the attachment is a .zip file, the copy of the worm may have one of the following second extensions:
     
     
   • .doc
   • .txt
   • .htm
   • .html
     
     
6. Connects to an IRC channel on the bleh.darkacidonline.us domain on TCP port 8080. The worm listens for commands that allow the remote attacker to perform the following actions:
   
   
   • Download files
   • Execute files
   • Delete files
   • Update itself
   • Get uptime information
     
     
7. Scans for vulnerable computers and tries to exploit the Microsoft Windows Local Security Authority Service Remote Buffer Overflow (described in Microsoft Security Bulletin MS04-011).
   
   
8. Blocks access to several security-related Web Sites by adding the following text to the Hosts file:
   
   127.0.0.1 www.symantec.com
   127.0.0.1 securityresponse.symantec.com
   127.0.0.1 symantec.com
   127.0.0.1 www.sophos.com
   127.0.0.1 sophos.com
   127.0.0.1 www.mcafee.com
   127.0.0.1 mcafee.com
   127.0.0.1 liveupdate.symantecliveupdate.com
   127.0.0.1 www.viruslist.com
   127.0.0.1 viruslist.com
   127.0.0.1 viruslist.com
   127.0.0.1 f-secure.com
   127.0.0.1 www.f-secure.com
   127.0.0.1 kaspersky.com
   127.0.0.1 www.avp.com
   127.0.0.1 www.kaspersky.com
   127.0.0.1 avp.com
   127.0.0.1 www.networkassociates.com
   127.0.0.1 networkassociates.com
   127.0.0.1 www.ca.com
   127.0.0.1 ca.com
   127.0.0.1 mast.mcafee.com
   127.0.0.1 my-etrust.com
   127.0.0.1 www.my-etrust.com
   127.0.0.1 download.mcafee.com
   127.0.0.1 dispatch.mcafee.com
   127.0.0.1 secure.nai.com
   127.0.0.1 nai.com
   127.0.0.1 www.nai.com
   127.0.0.1 update.symantec.com
   127.0.0.1 updates.symantec.com
   127.0.0.1 us.mcafee.com
   127.0.0.1 liveupdate.symantec.com
   127.0.0.1 customer.symantec.com
   127.0.0.1 rads.mcafee.com
   127.0.0.1 trendmicro.com
   127.0.0.1 www.microsoft.com
   127.0.0.1 www.trendmicro.com 

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. Disable System Restore (Windows Me/XP).
2. Update the virus definitions.
3. Run a full system scan and delete all the files detected as W32.Mytob.F@mm .
4. Delete any values added to the registry.
   

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

1. To disable 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

Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, reenable System Restore by following the instructions in the aforementioned documents.

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. To update 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 document: Virus Definitions (LiveUpdate).
• Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted daily. 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 document: Virus Definitions (Intelligent Updater).
  
  The latest Intelligent Updater virus definitions can be obtained here: Intelligent Updater virus definitions. For detailed instructions read the document: How to update virus definition files using the Intelligent Updater.
  
  Note: If you see an error, such as LU1418, when you try to run LiveUpdate and you cannot get the Web site hosting the Intelligent Updater, it is likely that the worm has modified the Hosts file. You can either download and install LiveUpdate 2.5, which can remove Symantec entries from that file, or you can edit it yourself. See the instructions for both in the "Additional Information" section below.

3. To scan for and delete 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.Mytob.F@mm, click Delete.
   
   Note: If your Symantec antivirus product reports that it cannot delete an infected file, Windows may be using the file. To fix this, run the scan in Safe mode. For instructions, read the document: How to start the computer in Safe Mode. Once you have restarted in Safe mode, run the scan again.
   
   After the files are deleted restart the computer in normal mode and proceed with section 4.
   

4. To delete the value from the registry
Important: 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 subkeys only. For instructions refer to the document: How to make a backup of the Windows registry.

1. Click Start > Run.
2. Type regedit
3. Click OK.
   
   
4. Navigate to the subkeys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersion
   RunServices
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_CURRENT_USERSoftwareMicrosoftOLE
   HKEY_CURRENT_USERSYSTEMCurrentControlSetControlLsa
   HKEY_LOCAL_MACHINESoftwareMicrosoftOLE
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlLsa
   
   
5. In the right pane, delete the value:
   
   "SVCHOST" = "taskgmr.exe"
   
   
6. Exit the Registry Editor.