Malicious Software Encyclopedia: Win32/Yaha
Published:
November 8, 2005
Win32/Yaha is a family of mass-mailing network worms that targets certain versions of Microsoft Windows. The worm spreads primarily by sending a copy of itself as an attachment to e-mail addresses gathered from an infected computer. It can also spread through mapped drives and writeable network shares. The worm can terminate security-related processes and conduct denial of service (DoS) attacks against certain Web sites.
On This Page
Threat Overview
| Class/type | Worm - Mass Mailer
Worm - Network
|
| Discovered | June 19, 2002 |
| Circulating | Yes |
| Affected operating systems | Windows NT 4.0
Windows 95
Windows 2000
Windows XP
|
| Affected software |
Not specified
|
| Infection rating | Low |
| Recovery difficulty | Easy |
| Damage rating | Low |
| 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):
McAfee:
W32/Yaha@MMSymantec:
W32.Yaha@mmTrend Micro:
WORM_YAHA.GEN
Learn more about the
Microsoft Virus Information Alliance.
Related Security Bulletins
The following Microsoft Security bulletins are related to this issue:
MS01-020 - Incorrect MIME Header Can Cause IE to Execute E-mail AttachmentMS01-027 - Flaws in Web Server Certificate Validation Could Enable SpoofingTechnical Analysis
When Win32/Yaha runs, it may take actions such as the following:
Drop multiple copies of itself with various names to locations such as <system folder>, %windir%, <recycle folder>. It also copies itself to <startup folder>.
Modify the registry as follows:
Create a value in registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
so that the worm runs each time Windows starts.
Create a value in each of the following keys:
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\exefile\shell\open\command
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\scrfile\shell\open\command
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\batfile\shell\open\command
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\piffile\shell\open\command
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\cmdfile\shell\open\command
so that the worm runs each time an executable file runs.
Spread through e-mail. The worm gathers e-mail addresses from the computer and saves them to a file. The worm sends a copy of itself as an e-mail attachment to those addresses. Due to an Internet Explorer vulnerability, the e-mail attachment can run automatically when the user previews or views the e-mail containing the attachment. Installing MS01-020 or MS01-027 patches this vulnerability, but the patch does not prevent the worm from running if the user opens the attachment.
Terminate processes and close windows for system utilities such as Task Manager.
Copy itself to all mapped drives.
Copy itself to all writeable network shares. It may add a line in the win.ini file on the network share host computer such as:
run = <worm copy file name>
Perform denial of service (DoS) attacks against certain Web sites.
Display several text messages in sequence or display an image of shaking words to look like a screensaver.
How to Prevent Infection
Take the following steps to help prevent infection on your system:
Enable a firewall on your computer.
Get the latest computer updates.
Use up-to-date antivirus software.
Use caution with unknown attachments.
Disconnect from unneeded mapped drives.
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 in Windows XP
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.
Disconnect from unneeded mapped drives
Malicious software can often spread over mapped network drives. Disconnect from drives mapped to your computer that you are not using.
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
There may be no readily apparent indications that your computer is infected by Win32/Yaha. However, your computer may be infected by this worm if you notice any of the following symptoms:
Presence of the value: "c:\recycled\msmdm" %1 %*"
in registry key HKEY_LOCAL_MACHINE\SOFTWARE\Classes\exefile\shell\open\command
Several text messages are displayed in sequence.
An image of shaking words that looks like a screensaver is displayed.
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 e-mail attachment to addresses that it finds on the computer. |
| Social Engineering | Can use a double extension for the attachment file name to make it appear that opening the attachment is safe. |
| Network Shares | Can spread to network shares by trying weak passwords. |
Payload Information
| Payload type | Trigger | Description |
|---|
| Compromises Security | Execution | - Terminates security-related processes.
- Closes windows for system utilities such as Task Manager.
|
| Display something | | Displays several text messages in sequence or displays an image of shaking words to look like a screensaver. |
| Creates files | | Creates copies of itself in various locations. |
