W32.Mydoom.B@mm

W32.Mydoom.B@mm is an encrypted mass-mailing worm that arrives as a message attachment using either a .exe, .scr, .cmd, or .pif extension. These files may be included as an attached .zip archive. The worm sends itself to all email addresses it locates in files on the system with the following extensions:
.htm
.sht
.php
.asp
.dbx
.tbb
.adb
.pl
.wab
.txt

It will avoid sending itself to addresses in any domain names containing the following strings:
avp
syma
icrosof
msn.
hotmail
panda
sopho
borlan
inpris
example
mydomai
nodomai
ruslis
.gov
gov.
.mil
foo.
berkeley
unix
math
bsd
mit.e
gnu
fsf.
ibm.com
google
kernel
linux
fido
usenet
iana
ietf
rfc-ed
sendmail
arin.
ripe.
isi.e
isc.o
secur
acketst
pgp
tanford.e
utgers.ed
mozilla

It also avoids sending itself to any of the following usernames:
root
info
samples
postmaster
webmaster
noone
nobody
nothing
anyone
someone
your
you
me
bugs
rating
site
contact
soft
no
somebody
privacy
service
help
not
submit
feste
ca
gold-certs
the.bat
page
admin
icrosoft
support
ntivi
unix
bsd
linux
listserv
certific
google
accoun

The worm may spoof the From address of the messages it sends. To do so, it takes random addresses it gathered above and adds one of the following usernames to the domain name:
sandra
linda
julie
jimmy
jerry
helen
debby
claudia
brenda
anna
alice
brent
adam
ted
fred
jack
bill
stan
smith
steve
matt
dave
dan
joe
jane
bob
robert
peter
tom
ray
mary
serg
brian
jim
maria
leo
jose
andrew
sam
george
david
kevin
mike
james
michael
alex
john

The message may have the following properties:
Subject may include the following:
Returned mail
Delivery Error
Status
Server Report
Mail Transaction Failed
Mail Delivery System
hello
hi

Message Body can be one of the following:
sendmail daemon reported:
Error #804 occured during SMTP session. Partial message has been received.

Mail transaction failed. Partial message is available.

The message contains Unicode characters and has been sent as a binary attachment.

The message contains MIME-encoded graphics and has been sent as a binary attachment.

The message cannot be represented in 7-bit ASCII encoding and has been sent as a binary attachment.

The attachment may be use one of the following filenames:
document
readme
doc
text
file
data
test
message
body

It may also use a double extension. If it does, the first extension will be one the following:
.htm
.txt
.doc

The attachment will always end with one of the following extensions:
.pif
.scr
.exe
.cmd
.bat
.zip

The icon used may be that of a text file if the extension is .exe or .scr, otherwise it uses the icon of an MS-DOS application.

When the attachment is executed, Notepad will open displaying garbage characters from the file %Temp%\Message dropped by the worm.

Next, it creates the following copy of itself:
%System%\explorer.exe

The worm then creates the following registry entries so that it executes every time Windows starts:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\Explorer = %System%\explorer.exe

HKEY_CURRENT_USER\Software\Microsft\Windows\CurrentVersion\Run\Explorer = %System%\explorer.exe

The worm will also modify the following registry entry so that it will be loaded by explorer.exe:
HKEY_CLASSES_ROOT\CLSID\{E6FB5E20-DE35-11CF-9C87-00AA005127ED}\InProcServer32\"(Default)" = "%System%\ctfmon.dll"

The following registry keys are also created:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer\ComDlg32\Version

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\ComDlg32\Version

The worm also copies itself to the user's Kazaa downloads directory using one of the following filenames:
xsharez_scanner
BlackIce_Firewall_Enterpriseactivation_crack
zapSetup_95_693
MS59-56_hotfix
winamp0
NessusScan_pro
attackXP-6.71

with one of the following extensions:
pif
scr
bat

If the shimgapi.dll file dropped by W32.Novarg.A@mm is present, the worm will delete it. It then drops the following file:
%System%\ctfmon.dll

This file appears to function as a back door that allows remote access to a compromised host on TCP ports 1080, 3128, 80, 8080, or 10080. Evidence suggests that this back door may also allow the compromised system to be used as a remote proxy.

The worm also appears to be capable of performing a denial of service attack on two distinct websites. If the compromised system date is greater than or equal to Feb 1, 2004, the worm will perform a DoS attack on www.sco.com. During the DoS attack, the worm creates 7 threads that invoke GET requests continuously for the main page of www.sco.com.

However, if the compromised system date is greater than or equal to Feb 3, 2004, the worm performs the DoS attack on www.microsoft.com. During this DoS attack, the worm creates 13 threads that invoke GET requests continuously for the main page of www.microsoft.com.

The worm continues its DoS attack until March 1, 2004.

The worm uses the hostname (i.e. www.sco.com and www.microsoft.com) and not a specific IP.

This variant also overwrites the HOSTS file in order to prevent the user from accessing various websites. Some of the websites include antivirus and security vendors, possibly to prevent the user from obtaining antivirus updates and fix tools. The following entries are added to the HOSTS file:
ad.doubleclick.net
ad.fastclick.net
ads.fastclick.net
ar.atwola.com
atdmt.com
avp.ch
avp.com
avp.ru
awaps.net
banner.fastclick.net
banners.fastclick.net
ca.com
click.atdmt.com
clicks.atdmt.com
dispatch.mcafee.com
download.mcafee.com
download.microsoft.com
downloads.microsoft.com
engine.awaps.net
fastclick.net
f-secure.com
ftp.f-secure.com
ftp.sophos.com
go.microsoft.com
liveupdate.symantec.com
mast.mcafee.com
mcafee.com
media.fastclick.net
msdn.microsoft.com
my-etrust.com
nai.com
networkassociates.com
office.microsoft.com
phx.corporate-ir.net
secure.nai.com
securityresponse.symantec.com
service1.symantec.com
sophos.com
spd.atdmt.com
support.microsoft.com
symantec.com
update.symantec.com
updates.symantec.com
us.mcafee.com
vil.nai.com
viruslist.ru
windowsupdate.microsoft.com
www.avp.ch
www.avp.com
www.avp.ru
www.awaps.net
www.ca.com
www.fastclick.net
www.f-secure.com
www.kaspersky.ru
www.mcafee.com
www.microsoft.com
www.my-etrust.com
www.nai.com
www.networkassociates.com
www.sophos.com
www.symantec.com
www.trendmicro.com
www.viruslist.ru
www3.ca.com

UPDATE: It appears that W32.Mydoom.B@mm scans for systems listening on TCP port 3127. This port is associated with the back door installed by W32.Novarg.A@mm (MCID 2468). If the worm finds a Novarg.A system listening on TCP port 3127, it will issue commands to terminate the worm and install Mydoom.B on the system.

*UPDATE: A previous conjecture regarding the possible failure of a denial of service routine targeted against www.microsoft.com, due to HOSTS file modifications has been proven false during ongoing analysis. The denial of service routine is fully functional.

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