Summary

Gismor is a mass-mailing worm that arrives in e-mail disguised as an MP3 player program. The worm uses the the Invalid MIME Type Vulnerability to execute the infected attachment automatically when the message is opened.

Additional Details

The message that Gismor sends has the following properties:

 From: MP3 Deluxe
 To: My best friends
 Subject: Phenomenal

The message has no text in the body and has an attachment called 'MP3Player.exe'.

When the infected attachment is run it copies itself to Windows System Directory as 'SSMS.EXE' and adds this copy to the registry as

 'HKCU\Software\Microsoft\Windows\CurrentVersion\Run\SSMS.EXE'

The worm uses MAPI to list all the incoming messages and sends an infected message to each sender it finds there. It uses direct SMTP connection to send the infected messages. The SMTP settings are fetched from the first active account from the user's settings. If the worm does not find the SMTP setting in the registry it uses a predefined SMTP server.

Payload

Gismor has a payload routine that overwrites certain files (.doc, .xls, .mp3, .mdb, .htm, .asp, .dbf, .cpp, .rtf, .wav) with the worm body. Based on the first analysis this routine is never called.

Notes

For more information and the fix for the Invalid MIME Type Vulnerabilty please visit

http://www.microsoft.com/windows/ie/downloads/critical/q323759ie/default.asp

[Analysis: Gergely Erdelyi; F-Secure Corp.; September 9th, 2002]