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F-Secure Malware Information Pages: Mytob.A
[Summary] | [Detailed Description]

Name : Mytob.A
Alias:Net-Worm.Win32.E77.a, W32/Mydoom.bg@mm
Type:Net-Worm, Worm
Category:Malware
Platform:Win32
Radar

Summary
A new worm Mytob.A which has MyDoom family functionality as well as borrows some of the bot family functionality has been spotted. The bot contains code to spread via network using LSASS vulnerability.
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Detailed Description
The worm is a PE executable file 42512 bytes long, packed with FSG file compressor.

Installation to system

When run, the worm copies under %SYSTEM% directory using the name 'msnmsgr.exe' and creates a mutex named 'D66'.

It will then alters the registry entries to ensure that it gets started when a user logs on or the system is restarted:

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run]
[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]
[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices]
[HKCU\SYSTEM\CurrentControlSet\Control\Lsa]
"MSN" = "msnmsgr.exe"

Spreading in e-mails

The worm spreads by sending its infected attachment to e-mail addresses found on an infected computer. E-mail addresses are harvested from Windows Address Book (WAB) and from files with the following extensions:
  • htm
  • sht
  • php
  • asp
  • dbx
  • tbb
  • adb
  • wab
  • pl
The worm avoids sending e-mails to e-mail addresses that contain any of the following substrings:

  • accoun
  • acketst
  • admin
  • anyone
  • arin.
  • be_loyal
  • berkeley
  • borlan
  • bugs
  • certific
  • contact
  • .edu
  • example
  • feste
  • fido
  • foo.
  • fsf.
  • gold-certs
  • google
  • .gov
  • gov.
  • help
  • hotmail
  • iana
  • ibm.com
  • icrosof
  • icrosoft
  • ietf
  • info
  • inpris
  • isc.o
  • isi.e
  • kernel
  • linux
  • listserv
  • math
  • .mil
  • mit.e
  • mozilla
  • msn.
  • mydomai
  • nobody
  • nodomai
  • noone
  • nothing
  • ntivi
  • page
  • panda
  • postmaster
  • privacy
  • rating
  • rfc-ed
  • ripe.
  • root
  • ruslis
  • samples
  • secur
  • sendmail
  • service
  • site
  • soft
  • somebody
  • someone
  • sopho
  • submit
  • support
  • syma
  • tanford.e
  • the.bat
  • unix
  • usenet
  • utgers.ed
  • webmaster
  • your

The e-mail message is composed from randomly chosen subject line, body text and additional parts. The worm has a selection of attachment
names that it uses for its attachment. The subject of infected e-mails is selected from the following variants:

  • Error
  • Status
  • Server Report
  • Mail Transaction Failed
  • Mail Delivery System
  • hello
  • hi

The attachment name is composed using predefined keywords. The keywords sets are:

  • body
  • message
  • test
  • data
  • file
  • text
  • doc
And extension keywords set are:

  • bat
  • cmd
  • exe
  • scr
  • pif

For example:

body.scr

Bot functionality

The worm tries to connect to IRC channel at predefined address using TCP port 6667. The attacker who knows channel password can instruct the created bot to execute the following actions:

  • Request worm uptime
  • Request worm version
  • Shutdown worm
  • Download and execute files
  • Delete files
  • Update worm
LSASS exploiting

The worm spreads to remote computers using LSASS vulnerability. It contacts remote computers on TCP port 445, exploits the vulnerability
and copies its file to a remote system.
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F-Secure Corporation

Last Modified: January 01, 2006