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  4. Bofra.C

Bofra.C

ALIAS:MyDoom.AG, I-Worm.Bofra.b

Summary

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

Additional 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]
 "Reactor3" = "%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.C 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.C 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 with the link: 

 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

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

Bofra.C, 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.C 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: 

 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

Backdoor

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

Detection

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

[FSAV_Database_Version]

Version=2004-11-09_01

Write-Up: Mikko Hypponen, November 9th, 2004;

Technical Details: Gergely Erdelyi, November 9th, 2004;

F-Secure Corporation