Threat description


Platform: W32


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.


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.

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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%\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   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.   


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


Hi! I am looking for new friends.  My name is Jane, I am from Miami, FL.  See my   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:

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 (  Checked for viruses by Gordano's AntiVirus Software  Checked by Dr.Web (   

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  

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

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


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