Summary

F-secure has raised alert level of this virus to Radar LEVEL 2:

Email Worm Sober.I is spreading, mostly in Europe. It sends highly variable German and English emails with an attachment. The virus drops several files to infected systems, including spool32dir.exe.

Additional Details

The worm is written in Visual Basic. The worm's file is a UPX packed PE executable with length of 56 KiBytes.

Installation to system

When the worm's file is started it shows the following messagebox:



Then the worm installs itself to system. It makes two copies itself to Windows System folder with a semi-randomly generated name and EXE extension. The following text strings are used to generate the file names of the worm's executable:

 sys
 host
 dir
 expoler
 win
 run
 log
 32
 disc
 crypt
 data
 diag
 spool
 service
 smss32

After that the worm creates startup keys for its files in Windows Registry. The key names are also semi-randomly generated from the above given list. The following keys are created:

 [HKCU\Software\Microsoft\Windows\CurrentVersion\Run]
 "<random>" = "%WinSysDir%\<random>.exe"
 [HKCU\Software\Microsoft\Windows\CurrentVersion\Run]
 "<random>" = "%WinSysDir%\<random>.exe %srun%"

 [HKLM\Software\Microsoft\Windows\CurrentVersion\Run]
 "<random>" = "%WinSysDir%\<random>.exe"
 [HKLM\Software\Microsoft\Windows\CurrentVersion\Run]
 "<random>" = "%WinSysDir%\<random>.exe %srun%"

During its installation cycle the worm creates the following files in Windows System folder:

 dgssxy.yoi
 sysmms32.lla
 cvqaikxt.apk
 Odin-Anon.Ger

These files have zero length and they are used to disable previous variants of Sober if they are installed on an infected computer.

Additionally the worm creates the following files:

  clonzips.ssc
  clsobern.isc
  nonzipsr.noz
  zippedsr.piz

These files are MIME-encoded copies of the worm's executable file and a ZIP archive with the worm's file. These files will be used for spreading of the worm in e-mail messages.

Spreading in e-mails

The worm sends e-mail messages with English and German texts and its file attached. The attached file can be an executable or a ZIP archive containing the worm's executable. The worm composes several different types of messages and the content of these messages is variable. Here's an example of a English message sent by the worm:



Before spreading the worm scans files with certain extensions on all hard disks to harvest e-mail addresses. Files with the following extensions are scanned:

 pmr
 stm
 slk
 inbox
 imb
 csv
 bak
 imh
 xhtml
 imm
 imh
 cms
 nws
 vcf
 ctl
 dhtm
 cgi
 pp
 ppt
 msg
 jsp
 oft
 vbs
 uin
 ldb
 abc
 pst
 cfg
 mdw
 mbx
 mdx
 mda
 adp
 nab
 fdb
 vap
 dsp
 ade
 sln
 dsw
 mde
 frm
 bas
 adr
 cls
 ini
 ldif
 log
 mdb
 xml
 wsh
 tbb
 abx
 abd
 adb
 pl
 rtf
 mmf
 doc
 ods
 nch
 xls
 nsf
 txt
 wab
 eml
 hlp
 mht
 nfo
 php
 asp
 shtml
 dbx

The found e-mail addresses and user names are saved in these 2 files that the worm created in Windows System folder:

 winroot64.dal
 winsend32.dal

When the worm is active in memory it blocks access to these files as well as to its MIME-encoded files and its executable file.

The worm ignores e-mail addresses that contain any of the following substrings:

 1-000000-000000
 tps@
 hubak@
 ruiv@
 farbugs@
 ron@
 info@
 sales@
 press@
 ventes@
 rar.dutch@
 rar@
 vmlich@
 jimaz@
 RAR.regsite@
 provision@
 alex@
 webmaster@
 rod@
 selwyn_arrow@
 admin@
 inftec@
 eugene@
 jwpark@
 sam@
 sites.far@
 whatsnew.far@
 helpdesk@
 fararcbugs@
 mark@
 cogswell@
 licensing@
 apply@
 Ollydbg@
 snaker@
 mail@
 qwaci@
 g-rom@
 lorian@
 stone@
 GOD@
 tac_2000@
 tac_cracking@
 mackt@
 christoph@
 -
 rarsoft.com
 rarsoft.de
 yahoo.com

If the worm sends infected messages to domains with suffixes '.de', '.ch', '.at', '.li' or to 'gmx.' domain, it composes messages in German, otherwise English messages are composed.

The worm can compose English messages from the following text string arrays:

Subject (one of the following):

 Details
 God it's
 Registration confirmation
 Confirmation
 Your Password
 Your mail password
 Delivery failure notice
 Faulty mail delivery
 Mail delivery failed
 Mail Error
 illegal signs in your mail
 invalid mail
 Mail Delivery failure
 mail delivery system

Message body (one of the following):

 I was surprised, too!
 Who could suspect something like that? shity

 Your password was changed successfully!
 Protected message is attached!

 This mail was generated automatically.
 More info about --<domain>-- under http://<domain>

Attachment name (one of the following):

 im_shocked
 thats_hard
 oh_nono
 user_info
 new_account
 info
 hostmaster
 corrected
 full
 original
 re_mail
 auto_mail
 mail

Sober's attachment name can contain a random number and can have one of the following extensions:

 .com
 .bat
 .pif
 .scr

Also the attachment can be sent in a ZIP archive. In this case the worm's file inside the archive will have double extension. The first extension is selected from the following list:

 .txt
 .doc
 .word
 .xls
 .eml

The subject of an infected e-mail can have 'FwD:' or 'Re:' string.

Sober.I can place a fake anti-virus scanner report in the message body trying to persuade a recipient that the message was scanned by an on-line scanner and no infection was found.

Detection

This Sober variant is detected with FSAV updates:

Version=2004-11-19_01

Technical Details: Jarkko Turkulainen; November 19th, 2004;

Write-up: Katrin Tocheva; November 19th, 2004;