W32.Appix.Worm

When W32.Appix.Worm runs, it performs the following actions:

It drops itself using the following file names:

• %windir%\Appboost.exe
• %windir%\Appbsvc.exe

NOTE: %windir% is a variable. The worm locates the Windows main installation folder (by default this is C:\Windows or C:\Winnt) and uses it as a destination folder.

The worm creates the vix or vixsvc mutex. This allows only one instance of the worm to execute in memory.

The worm updates the (Default) value of the key

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\exefile\shell\open\command

with the following contents:

%windir%\appboost.exe "%1" %*

so that it runs whenever an .exe file is executed.

It also creates the value

<random digit, e.g. 6>    <time when the worm was executed in an internal format>

in the registry key

HKEY_CURRENT_USER\Software\Microsoft\Mails

The worm tries to disable some antivirus and firewall programs by terminating the active processes and stopping the active services. This is the list of processes that the worm terminates:

• _AVP32
• _AVPCC
• NOD32
• NPSSVC
• NRESQ32
• NSCHED32
• NSCHEDNT
• NSPLUGIN
• NAV
• NAVAPSVC
• NAVAPW32
• NAVLU32
• NAVRUNR
• NAVW32;
• _AVPM
• ALERTSVC
• AMON
• AVP32
• AVPCC
• AVPM
• N32SCANW
• NAVWNT;
• ANTIVIR
• AVPUPD
• AVGCTRL
• AVWIN95
• SCAN32
• VSHWIN32
• F-STOPW;
• F-PROT95
• ACKWIN32
• VETTRAY
• SWEEP95
• PCCWIN98
• IOMON98
• AVPTC
• AVE32
• AVCONSOL
• FP-WIN
• DVP95
• F-AGNT95
• CLAW95
• NVC95
• SCAN
• VIRUS
• LOCKDOWN2000
• NORTON
• MCAFEE
• ANTIVIR
• FIREWAL
• VET95

If the operating system is Windows 95/98/Me, the worm registers itself as a service process so that it continues to run after you log off. In this case, W32.Appix.Worm will close only when the system is shut down.

If the operating system is Windows NT/2000/XP, the worm creates the appboost service, adds it to the service control manager database, and starts it. The service has the display name "Application Boost Service."

W32.Appix.Worm then composes the file name, which consists of three parts:

The first part is randomly chosen from the following list (spelling errors are preserved):

• Adobe Photoshop
• Paintshop Pro
• Windows XP Coprate
• Windows XP Proffesional
• Office XP
• Quake 3 Online
• Counter Strike Online
• Unreal Tournament Online
• Unreal Tournament 2003 Online
• Soldier of Fortune Online
• Soldier of Fortune
• XBOX Emulator
• PS2 Emulator
• GameCube Emulator

The second part is randomly chosen from the following list:

• Key Generator
• Serial Generator
• Crack

The third part, which is an extension, is selected randomly from this list:

• .zip.exe
• .rar.exe
• .ace.exe
• .rar.exe
• .exe
• .pif
• .cmd
• .bat
• .hta

As a result, the composed file name may look this: Adobe Photoshop Crack.rar.exe

The worm then copies itself using the composed file name into the shared folders of the KaZaA and Edonkey2000 software. If it finds a folder named Download or Downloads on drives C and D, it drops itself there, as well.

The worm contains its own SMTP client engine, which allows it to submit itself in the form of an email message. The worm exploits a vulnerability in Microsoft Outlook and Outlook Express in an attempt to execute itself when you open or even preview the message in which it is contained. Information and a patch for the vulnerability are available at http://www.microsoft.com/technet/security/bulletin/MS01-020.asp.

The worm contains code that may construct and submit an email message in the following form:
Attachment: Test.scr (175,112 bytes or 176,128 bytes)
Subject: test23

The worm enumerates files on fixed drives C and D. If it locates a PHP or PHTML file, it appends it with a PHP script (PHP is a server-side scripting language that is used for dynamic Web page generation). The infected PHP/PHTML files are detected by Symantec antivirus product as PHP.Appix.

The viral PHP-script enumerates files that exist in the same folder as the infected file and infects other PHP and PHTML files by appending itself. The infection is not performed, if the infection marker is found. For every HTM or HTML file, it appends an exploit code that may cause your browser or the operating system to stop responding. The exploit code is based on infinite loops that consume resources. It may also perform a DoS attack against one of the Web sites. The viral PHP code is designed to upload the W32.Appix.Worm executable to the client computer that visits the infected Web site. It exploits the "File Name Spoofing Vulnerability." Information and a patch for the vulnerability are available at http://www.microsoft.com/technet/security/bulletin/MS01-058.asp.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
• 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.
• Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
• Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
• Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
• Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
• If a 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate compromised computers quickly to prevent threats from spreading further. 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.
• If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
• For further information on the terms used in this document, please refer to the Security Response glossary.

Summary