Threat Descriptons



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Zotob.C is a new variant of Zotob. It spreads using a vulnerability in Windows Plug and Play service (MS05-039) and ASN.1 (MS04-007). This variant also has Mydoom email spreading routine.


Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note: You need administrative rights to change the settings.

Technical Details

The worm is a packed PE executable file 31744 bytes long.

Installation to system

When run, the worm copies under %SYSTEM% directory using the name 'per.exe' and creates a named mutex 'B-O-T-Z-O-R' for making sure that only one copy of the worm is run at the same time.

Then it adds the following registry entries to ensure that it is started when a user logs on or the system is restarted:

  • [HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]
  • [HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices] "WINDOWS SYSTEM" = "per.exe"

The worm also adds the following registry key for diasabling shared access service:

  • [HKLM\SYSTEM\CurrentControlSet\Services\SharedAccess] "Start" = "4"

Email spreading

The worm can spread by sending its infected attachment to email addresses found on an infected computer. email addresses are harvested from Windows address book and from files with the following extensions:

  • txt
  • htm
  • sht
  • jsp
  • cgi
  • xml
  • php
  • asp
  • dbx
  • tbb
  • adb
  • wab
  • pl

The worm avoids sending emails to email addresses that contain any of the following substrings:

  • avp
  • syma
  • icrosof
  • msn.
  • hotmail
  • panda
  • sopho
  • borlan
  • inpris
  • example
  • mydomai
  • nodomai
  • ruslis
  • .gov
  • gov.
  • .mil
  • foo.
  • berkeley
  • unix
  • math
  • mit.e
  • fsf.
  • google
  • kernel
  • linux
  • fido
  • usenet
  • iana
  • ietf
  • rfc-ed
  • sendmail
  • arin.
  • ripe.
  • isi.e
  • isc.o
  • secur
  • acketst
  • tanford.e
  • utgers.ed
  • mozilla
  • be_loyal:
  • root
  • info
  • samples
  • postmaster
  • webmaster
  • noone
  • nobody
  • nothing
  • anyone
  • someone
  • your
  • bugs
  • rating
  • site
  • contact
  • soft
  • somebody
  • privacy
  • service
  • help
  • submit
  • feste
  • gold-certs
  • the.bat
  • page
  • admin
  • icrosoft
  • support
  • ntivi
  • unix
  • linux
  • listserv
  • certific
  • google
  • accoun
  • fcnz
  • secur
  • abuse

The email message is composed from randomly chose subject line, body text and additional parts. The worm has a selection of attachment names that it uses for its attachment. The subject of infected emails are selected from the following variants:

  • Warning!!
  • **Warning**
  • Hello
  • Confirmed...
  • Important!

Body of the text is selected from the following list:

  • looooool
  • We found a photo of you in ...
  • That's your photo!!?
  • hey!!
  • 0K here is it!

The attachment name is composed using predefined keywords. The keywords set is:

  • photo
  • your_photo
  • image
  • picture
  • sample
  • loool
  • webcam_photo

And extension keywords set are:

  • bat
  • cmd
  • exe
  • scr
  • pif

Spreading using exploits

The worm scans for systems vulnerable to Microsoft Windows Plug and Play service (MS05-039) and ASN.1 vulnerability (MS04-007) through TCP/445.

It creates 200 threads that connect to random IP addresses within the B-class ( network of the infected system. First it tests connection to port 445 and if successful, it tries to exploit the PnP vulnerability. If the attack is successful, a shell (cmd.exe) is started and FTP script is transferred and executed on the remote machine. This script then downloads and executes the worm's file from the attacking machine. Please see the details of this attack from Zotob.A description:


If the PnP attack fails, the worm tries to exploit ASN.1 vulnerability (MS04-007). The attack is very similair to PnP attack - an FTP script is executed on a remote host and the built-in FTP server is then used to transfer the worm's file to exploited system. ASN.1 exploit is reported to work on (unpatched) Windows 2000 SP 2-4 and Windows XP SP 0-1.

Please see the following pages for detailed information on the vulnerabilities:


Bot functionality

The worm tries to connect to IRC channel at predefined address. The attacker who knows channel password can instruct the bot to execute the following actions:

  • Disconnect/reconnect from the IRC channel
  • Request system information
  • Download and execute files
  • Remove worm from the system
  • Manipulate system security settings

Additional details

Zotob.C modifies system hosts file in order to disable access to certain sites. Following hostnames are redirected to localhost IP address (


The worm also writes the following text to hosts file:

  • Botzor2 pnp+asn+mail spread. Greetz to good friend Coder. Based On HellBot3 f-secure,sophos ok wait bitchs!!!

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