Summary

A new Sober.E worm was found in Germany on Sunday March 28th, 2004. The worm replaces the 'From:' filed so the infected email looks like it comes from @gmx.net or @gmx.de address. The size of the worm's file is 30720 bytes (PIF file) or 30866 bytes (ZIP archive).

Additional Details

The worm is written in Visual Basic. The worm's file is a PE executable 30720 bytes long packed with a modified version of UPX file compressor. The worm has its own SMTP engine that it uses to send out infected e-mail messages.

The worm changes one byte at offset 0xA0 in its file upon installation to system, but the file it sends out is unchanged.

Some of the worm's text strings are encrypted and they are decrypted only before being used.

Installation to system

When the worm's file is started on a clean system, it opens Paintbrush or Microsoft Paint application as a disguise.

Then the worm installs itself to system. It copies itself to Windows System folder once, with a semi-randomly generated name and creates 2 startup keys for this file in System Registry. The worm uses the following fixed text strings to generate the name of its file and the name of the startup key:

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

The worm creates a file named WINRUN32.DLL, where it stores all e-mail addresses harvested from an infected computer. The worm also creates 2 empty files in the same folder:

 zmndpgwf.kxx
 bcegfds.lll

Additionally the worm creates 2 mime-encoded copies of its executable file and a ZIP archive in Windows System folder with the following names:

 msWord.wrd
 MsHelp32.dat

The worm creates 2 startup Registry keys its semi-randomly named file in System Registry:

 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]
 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce]

The subkey name that is created by the worm is semi-randomly generated too. The value of a subkey is the path the worm's file in Windows System folder.

Spreading in e-mails.

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

 ini
 log
 mdb
 tbb
 abd
 adb
 pl
 abx
 rtf
 doc
 xls
 txt
 wab
 eml
 php
 asp
 shtml
 dbx

The worm saves all found e-mail addresses to WINRUN32.DLL file located in Windows System folder. This is an ASCII file, not a binary file.

Sober.E worm spreads itself in e-mails as an executable attachment or inside a ZIP archive. The worm uses the following strings as the subject line:

 Hi
 hi
 Hi :-)
 Ok :-)
 OK OK
 Ok ok OK!
 Hey!
 hey?
 HEY

The message body can contain the following strings:

 thx
 Thx!
 THX
 ;-)
 ha!
 HA
 yo!
 lol
 LoL
 LOL
 Yo!

The attachment name can consist of the following strings and a randomly generated number:

 text
 read
 Graphic-doc
 document
 worm

The attachment has either PIF or ZIP extension. The worm's executable file name inside the archives that we've received so far is:

 Graphic_Textdocument.pif

To send e-mails the worm uses the following mail servers:

 mail.gmx.net
 mail.gmx.de

The worm fakes the sender's e-mail address. The fake address is composed by the worm from the following strings:

 aRuder
 g.rulers
 S.Serger
 Dude-X777
 Nicole.Pam
 R.Summer
 T.Welder
 Susan.Ewing
 E.Ruders
 Blond.Sybil
 Michelle.Horn
 Sabine.S-1977
 E.Juller
 Pamela-S
 J.Moders
 Regina-1978
 BMueller4
 Elsbeth.Sinker
 Thomas.Schmahler
 Nikki.1978
 D.Rotter
 Patricia.1979
 S.Loltke
 Patty.Geldorf
 H.Molma
 Birgit.Muse
 Peter.Selders
 Johanna.1980
 Nicole.Gellert
 R.Niere
 P.Schulz1
 Kalif.Rent
 Herbert.Weed
 FParker
 Samatha.Kelis
 Kate.Lee
 Bibi.Besen
 Julia.Witt1
 Alexander.Bendher
 Rosemarie.Hetter
 A.Rebert
 Elke.Duerr
 D.Winter1
 Angelika.Neum
 A.Kempen
 KevinEder
 Susan.Leet
 Friedhelm.alt
 Seth.Liveima
 Eileen.Leen
 D.Augustam
 B.Kaine
 MikeLord
 Kathe.Meet
 Marie.Dreher
 Tom.Schon
 Lisa.Redfield
 R.Kleinmaurer
 A.Mack1
 Jundel
 b.sieber006
 Ulrike.Falkner
 C.Poller

The following domain names are selected for the fake sender's address:

 @gmx.net
 @gmx.de

The worm avoids sending infected messages to e-mail addresses that contain any of the following:

 bigfoot
 hotmail
 online
 web
 accor
 yahoo
 gmx
 aol
 msn

Additional information

Sober.E worm constantly checks a hard drive for the presence of the file named ZHCARXXI.VVX. If this file is found, the worm unloads itself from memory. Also if this file is present on a hard disk during the worm's installation process, the worm does not copy itself to a hard drive.

The worm can download and run an executable file from the following websites:

 home.acror.de
 people.freenet.de

The name of the downloaded file is:

 ndhaqqth.exe

The worm tries to contact several NTP servers that are hardcoded it its body:

 Rolex.Peachnet.edu
 ntps1-1.cs.tu-berlin.de
 ntp2.fau.de
 ptbtime2.ptb.de
 time.nrc.ca
 ntp.metas.ch
 ntps1-0.cs.tu-berlin.de
 ntp0.fau.de
 timelord.uregina.ca
 ntp-1.ece.cmu.edu
 ptbtime1.ptb.de
 time.ien.it
 ntp3.fau.de
 time.chu.nrc.ca
 clock.psu.edu
 ntp1.fau.de

Detection

Detection of Sober.E worm is available in the following FSAV updates:

[FSAV_Database_Version]
Version=2004-03-28_01

Writeup: Katrin Tocheva, March 28th, 2004;

Technical Details: Alexey Podrezov; March 28th, 2004;

Description Updated: Alexey Podrezov; March 29th, 2004;