Zafi.F

Zafi.F spreads in FSG! packed form which is 16770 bytes in size. The body unpacks to around 30 KiB of hand-written assembly code.

System Infection

When Zafi.F is started it copies itself to the Windows System Directory with a name "AntiVirus Update.exe". This file is added to the following registry key:

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run] "Zi5" = "%System%\AntiVirus Update.exe"

Zafi.F creates a mutex named "Zi5" for making sure that only one copy of the worm is run at the same time.

Zafi.F enumerates all the directories in the system and copies itself as either 'Adobe Acrobat 8.0 Pro.exe' or 'Windows Update Crack.exe' to the ones that contain 'shar', 'uploa' or 'musi' in their name.

Email Propagation

Zafi.F looks into the Windows Address Book and different files and tries to gather email addresses. Files with the following extensions are checked:

• dbx
• asp
• txt
• htm
• mbx
• wab
• php
• sht
• adb
• tbb
• inb
• pmr
• fpt
• eml

Using its own SMTP engine the worm sends messages with infected attachments in many different languages. It can use different SMTP relays for sending its messages depending on the language.

For email addresses in the following domains the worms sends messages in the respective languages:

.hu .sp .se .de .at .ch .nl .fr .it .es .mx .ru

Following text is an example of english message:

From: M. Christina Subject: msn photo ecard commercial ecard :))

Sender name is used as a fallback if the email address doesn't have it.

Other language versions are as follows:

From: Szalai Bernadett Subject: legszexibb megasztar foto! szavazz ra te is! From: N. Fernandez Subject: broma :)) humor :)) From: H. Andersson Subject: rolig reklam :)) haha - rolig :)) From: H. Maria Subject: witzig reklame :)) witzig bild :D From: R. Cornel Subject: grappig beeld :)) een grappig reclame :DFrom: B. Martin Subject: blague :)) humour - reclame :)) From: R. Antonio Subject: scherzo :)) comico quadro :)) From: N. Fernandez Subject: broma :)) humor :)) From: D. Alexej Subject: humor.ru :D The body message is ImageFormat: 640x480 ImageSize: 16Kb Message: you need to see this :)) From: Date: AV-Control: MSN Mail: +++ No Virus

The actual attachment is a ZIP file with name composed of the following words:

• reklam
• megasztar
• humor
• reklame
• reclame
• funny
• commercial

Inside the ZIP file, there is a copy of the worm using one of the following file extensions:

• .bat
• .cmd
• .com
• .pif

Here's a screenshot of English message:

The worm does not send emails to addresses that contain any of these strings:

• admi
• bitde
• contact@
• eset
• -faq
• google
• help
• hotmai
• info
• linux
• kasper
• mcafe
• micro
• msn
• nod3
• panda
• sales
• secur
• service
• soft
• sopho
• subsc
• suppor
• support
• symant
• test
• trend
• use
• webm
• win
• www

Payload

Zafi.F terminates any application that has the words 'firewall' or 'virus' in it. These files are overwritten with a copy of the worm.

Several Windows tools, like Task Manager, Registry Editor are disabled when the worm is active. Zafi.F opens these files with exclusive locking to prevent anything else from opening them.

Zafi.F has a backdoor that listens on port 2121. The worm can upload and execute file using the backdoor.