Bofra.B

Summary

The Bofra.B worm appeared on November 9th, 2004. This worm exploits an unpatched vulnerability in Internet Explorer's IFRAME handling. Unlike regular mass-mailing worms, Bofra.B 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.B has an IRC-controlled backdoor that allows the creator to download and execute arbitrary programs on the compromised host.

Disinfection & Removal

Allow F-Secure Anti-Virus to disinfect the relevant files.

For more general information on disinfection, please see Removal Instructions.

Technical Details

The worm's body is a Windows PE executable file compressed with the MEW executable compressor. The unpacked body is around 42 KiB and was most likely hand-coded in assembly.

System Infection

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

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run]
 "Reactor5" = "%SystemDir%\<randomname>32.exe"

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

Email Propagation

To gather email addresses Bofra.B 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.B sends emails to the collected addresses. Sender of the mails is spoofed and the content is randomly chosen from the following components:

Email subjects:

Confirmation
 Hello!
 Hey!
 Hi!

Email bodies contain an HTML-formatted text with the link:

Congratulations! PayPal has successfully charged $175 to your credit card.
 Your order tracking number is A866DEC0, and your item will be shipped
 within three business days
 To see details please click this <link>
 DO NOT REPLY TO THIS MESSAGE VIA EMAIL! This email is being sent by
 an automated message system and the reply will not be received.

or

Hi! I am looking for new friends. I am from Miami, FL.
 You can see my <homepage> with my last webcam photos!

or

Hi! I am looking for new friends.
 My name is Jane, I am from Miami, FL.
 See my <homepage>  with my weblog and last webcam photos!
 See you!

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

h**p://<infected host ip>:port/<file_to_dowload>

Bofra.B, 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.B 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, among them:

accoun
 certific
 listserv
 ntivi
 support
 icrosoft
 admin
 page
 the.bat
 gold-certs
 ca
 feste
 submit
 not
 help
 service
 privacy
 somebody
 no
 soft
 contact
 site
 rating
 bugs
 me
 you
 your
 someone
 anyone
 nothing
 nobody
 noone
 webmaster
 postmaster
 samples
 info
 root

Backdoor

As a payload Bofra.B has an IRC-controlled backdoor that allows the creator to download and execute arbitrary programs on the compromised host.

Detection

Detection for Bofra.B was published on November 9th, 2004 in the following F-Secure Anti-Virus updates:

Detection Type: PC
Database: 2004-11-09_01

Description Created: Mikko Hypponen, November 9th, 2004
Technical Details: Gergely Erdelyi, November 9th, 2004