F-Secure Virus Descriptions : Bofra.A

[Summary] | [Detailed Description] | [Detection]

NAME:	Bofra.A
ALIAS:	MyDoom.AI, I-Worm.Bofra.a

Summary

Bofra.A worm appeared on November 10th, 2004. This worm exploits an unpatched vulnerability in Internet Explorer's IFRAME handling. Unlike regular mass-mailing worms, Bofra.A does not send itself in the emails, only an HTTP link that points to the host that sent the infected email.

As a payload Bofra.A has an IRC-controlled backdoor that allows the worm's author to download and execute arbitrary programs on the compromised host.

Detailed Description

The worm's body is a Windows PE executable file compressed with the MEW executable compressor and was patched by PE_Patch utility.

System Infection

When the worm's file is run, it copies itself to Windows System Folder with a random name ending in '32.exe' (for example pmbperim32.exe) and creates a startup key for this file in the Registry:

 [HKLM\Software\Microsoft\Windows\CurrentVersion\Run]
 "Rhino" = "%SystemDir%\<randomname>32.exe"

where "%SystemDir%" represents the Windows System folder name, for example "C:\Windows\System32\" on Windows XP systems.

Email Propagation

To gather email addresses Bofra.A searches the Windows Address Book, files in Temporary Internet File and other files on the hard disk that have the following strings in their name:

 wab
 pl
 adb
 tbb
 dbx
 asp
 php
 sht
 htm
 txt

Using its own SMTP engine Bofra.A sends emails to the collected addresses. Sender of the mails is spoofed and the content is randomly chosen from the following components:

Email subjects:

 funny photos :)
 hello
 hey!

Email bodies contain an HTML-formatted text:

 FREE ADULT VIDEO! SIGN UP NOW!

 Look at my homepage with my last webcam photos!

The email does not have any attachments. The worm only sends the link which points to the infected host. The format of the link is

 http://<infected host ip>:port/<file_to_dowload>

Bofra.A, running on the infected host, has a stripped-down web servers listening on TCP ports starting from 1638 (0x666). The only purpose of these is to serve the potential targets with the HTML page that contains the exploit as well as the worm executable that the exploit will download.

The way this propagation technique works in explained in our weblog:

http://www.f-secure.com/weblog/archives/archive-112004%2ehtml#00000347

The emails sent by Bofra.A contain a fake virus scanner header (X-AntiVirus:) that might get one of the following values:

 scanned for viruses by AMaViS 0.2.1 (http://amavis.org/)
 Checked for viruses by Gordano's AntiVirus Software
 Checked by Dr.Web (http://www.drweb.net)

The worm avoids posting to e-mail addresses that contain certain strings:

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

The worm fakes the sender's address. It uses the following list of names to compose the fake address:

 john
 john
 alex
 michael
 james
 mike
 kevin
 david
 george
 sam
 andrew
 jose
 leo
 maria
 jim
 brian
 serg
 mary
 ray
 tom
 peter
 robert
 bob
 jane
 joe
 dan
 dave
 matt
 steve
 smith
 stan
 bill
 bob
 jack
 fred
 ted
 adam
 brent
 alice
 anna
 brenda
 claudia
 debby
 helen
 jerry
 jimmy
 julie
 linda
 sandra

The worm uses the following list of domain names to compose the fake sender's address:

 aol.com
 msn.com
 yahoo.com
 hotmail.com

Backdoor

As a payload Bofra.A has an IRC-controlled backdoor that allows the worm's author to download and execute arbitrary programs on the compromised host.

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Detection

Detection for Bofra.A was published on November 10th, 2004 in the following F-Secure Anti-Virus update:

[FSAV_Database_Version]

Version=2004-11-10_03

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Technical Details: Gergely Erdelyi and Alexey Podrezov, November 10th, 2004;

F-Secure Corporation