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.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
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
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.
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.
For more information and the fix for the Invalid MIME Type Vulnerabilty please visit
Technical Details: Gergely Erdelyi; F-Secure Corp.; September 9th, 2002