Sober.E

Threat description

Details

CATEGORYMalware
TYPEWorm

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).

Removal

Automatic action

Depending on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the suspect file, or ask you for a desired action.

More scanning & removal options

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You may also refer to the Knowledge Base on the F-Secure Community site for more information.

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Technical 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:

Detection Type: PC

Database: 2004-03-28_05

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