Malicious Software Encyclopedia: Win32/Mytob
Published:
May 1, 2007
Win32/Mytob is a family of mass-mailing worms that targets computers running certain versions of Microsoft Windows. The worm can spread by exploiting Windows vulnerabilities that are fixed by installing Microsoft Security Updates MS03-026 and MS04-011. The worm can also spread by sending a copy of itself through e-mail, MSN Messenger, or Windows Messenger.
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Threat Overview
| Class/type | Worm - Mass Mailer
|
| Discovered | April 1, 2005 |
| Circulating | Yes |
| Affected operating systems | Windows NT 4.0
Windows 95
Windows 2000
Windows XP
|
| Affected software |
Not specified
|
| Infection rating | High |
| Recovery difficulty | Moderate |
| Damage rating | Medium |
| Transmission rating | Medium |
Aliases (Also Known As)
Different antivirus vendors may be using different names to refer to this malicious software. Here are some of the names currently in use by antivirus software vendors participating in the Microsoft Virus Information Alliance (VIA):
CA:
Win32/AtakF-secure:
MytobMcAfee:
Win32/MytobSymantec:
W32.MytobTrend Micro:
WORM_MYTOB
Learn more about the
Microsoft Virus Information Alliance.
Related Security Bulletins
The following Microsoft Security bulletins are related to this issue:
MS03-026 - Buffer Overrun In RPC Interface Could Allow Code Execution (823980)MS04-011 - Security Update for Microsoft Windows (835732)Technical Analysis
Win32/Mytob can spread in several ways:
By sending a copy of itself as an e-mail attachment to addresses gathered from an infected computer and from Web site queries.
By sending a copy of itself in a message using MSN Messenger or Windows Messenger.
By copying itself to writeable network shares that have weak passwords.
By exploiting the DCOM RPC buffer overflow vulnerability that is fixed in Microsoft Security Bulletin MS03-026. This vulnerability allows an attacker to send and run a copy of the worm to other computers.
By exploiting the LSASS buffer overflow vulnerability that is fixed in Microsoft Security Bulletin MS04-011. This vulnerability allows an attacker to send and run a copy of the worm to other computers.
When Win32/Mytob runs, it may take the following actions on the infected computer:
Send e-mail to those addresses, attaching a copy of itself. The e-mail contains a fabricated sender, subject line, message body text, and attachment name. The worm runs when a user opens the e-mail attachment that contains the worm.
How to Prevent Infection
Take the following steps to help prevent infection on your computer:
Enable a firewall on your computer.
Get the latest computer updates.
Use up-to-date antivirus software.
Use caution with unknown attachments.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows XP Internet Connection Firewall.
To turn on the Internet Connection Firewall in Windows XP
Click Start, and click Control Panel.
Click Network and Internet Connections, and click Network Connections. If you do not see Network and Internet Connections, click Switch to Category View.
Highlight a connection that you want to help protect, and click Change settings of this connection.
Click Advanced, and select Protect my computer and network by limiting or preventing access to this computer from the Internet.
Click OK.
Get the latest computer updates
Updates help protect your computer from viruses, worms, and other threats as they are discovered. You can use the Automatic Updates feature in Microsoft Windows XP to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
To turn on Automatic Updates
Click Start, and click Control Panel.
Click Performance and Maintenance. If you do not see Performance and Maintenance , click Switch to Category View.
Click System.
Click Automatic Updates, and select Keep my computer up to date.
Select a setting. Microsoft recommends selecting Automatically download the updates, and install them on the schedule that I specify and setting a regular update time.
If you choose to have Automatic Updates notify you in step 5, you will see a notification balloon when new downloads are available to install. Click the notification balloon to review and install updates.
Use up-to-date antivirus software
Most antivirus software can detect and prevent infection by known malicious software. You should always run antivirus software on your computer that is updated with the latest signature files to automatically help protect you from infection. If you don't have antivirus software installed, you can get it from one of several companies. For more information, see http://www.microsoft.com/athome/security/downloads/default.mspx
Use caution with unknown attachments
Use caution before opening unknown e-mail or IM attachments, even if you know the sender. If you cannot confirm with the sender that a message is valid and that an attachment is safe, delete the message immediately, and run up-to-date antivirus software to check your computer for viruses.
Use strong passwords
A strong password has at least eight characters and includes a combination of letters, numbers, and symbols. It is easy for you to remember, but difficult for others to guess. Weak passwords include any words in the dictionary, names, dates, consecutive letters or numbers, common words with symbol substitutions (for example, p@ssw0rd), and so on.
Remove unneeded network shares
Malicious software can often spread over network shares. Remove unneeded network shares that are mapped to your computer.
To remove network shares in Windows XP
On the Start menu, click My Computer.
On the Tools menu, click Disconnect Network Drives…
In the Disconnect Network Drives dialog box, click the drives to disconnect and click OK.
How to Tell If Your Computer Is Infected
How to Recover from Infection
Automatic Recovery
To attempt to automatically remove this threat, run one of the following removal tools:
Transmission Methods
| Method | Description |
|---|
| Mass Mailer | Sends itself as an attachment to e-mail addresses from the computer and from Web site queries. |
| Exploits Vulnerability | Exploits the DCOM RPC buffer overrun vulnerability, fixed in MS03-026, or the LSASS buffer overrun vulnerability, fixed in MS04-011. |
| Network Shares | Copies itself to remote, writeable network shares with weak passwords. |
| Social Engineering | Sends itself to contacts using MSN Messenger or Windows Messenger. |
Payload Information
| Payload type | Trigger | Description |
|---|
| Sends e-mails | Execution | Sends itself as an attachment to e-mail addresses on the computer and from Web site queries. |
| Compromises Security | Execution | Connects to an IRC server to receive commands from attackers. |
| Creates files | Execution | Creates file <system folder>\msnmsgr.exe or file <temp folder>\msnmsgr.exe. |
