Channel Strategies for the CIOCustomers may not know the difference between a virus and a worm, but understanding the different types of malware will help you protect their systems -- and pass the SSCP certification exam. This
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excerpt, from the Official (ISC)²® Guide to the SSCP® CBK® Domain 7: Malicious Code, by Diana-Lynn Contesti, takes a look at double file extensions. Download the full Domain as a PDF to learn about the different types of malware and their payloads.
Viruses, worms and Trojan horses all make use of the double file extension. The Windows operating systems allows the creation of files names with a number of spaces in it. This trick is intended to fool users into believing that the file they are viewing cannot be executed. as in this example:
PLAIN.TXT.EXE
The .EXE at the end of the spaces, makes the program executable. Unfortunately in e-mail, users will only see the .TXT and potentially believe that the file is simply a Text file. This is why much has been done to educate users on not running e-mail attachments.
As a number of file extensions can be used to deliver or contain malicious code, it is recommended that the administrators block specific File Extensions at the Firewall. Table 7.3 is a partial list of suggested file extensions that should be blocked.
It is difficult for end users to understand all the file extensions that can be used and those that may be considered dangerous or Executable. Therefore, it is a good idea to develop a list of extensions that will be blocked at the Firewall by default. Every organization is unique and the list that is correct for one organization may not be correct for another. It is a good idea to educate users on some of the basic file extensions that you may not be able to block (i.e., .EXE, .PIF, .SCR, .COM).
A complete list of file extensions and their meanings is available at The File Extension Source; also view Every File Extension in the World from WhatIs.com.
Table 7.3 A Partial List of File Extensions That Should Be Blocked
| File Extension | Descriptions |
|---|---|
|
|
Acrobat Plug-in Used to view Adobe Acrobat files |
|
|
Batch processing file Used to execute a series of commands in a sequential order |
|
|
Borland package libraries Used in programs developed with the Delphi software language |
|
|
Compiled HTML Help file Could include a link that would download and execute malicious code |
|
|
Command File Contains scripts and executables for DOS or Windows |
|
|
Dynamic Link Library Executable code that is shared by other programs on the system |
|
|
Device Driver Used to extend the hardware support of a Windows machine |
|
|
Windows binary executable program |
|
|
Object linking and embedding (OLE) control Used to orchestrate the interaction of several programs on a Windows machine |
|
|
Program Information File Used to tell windows how to run non-Windows applications |
|
|
Screen saver programs Includes binary executable code |
|
|
System configuration file Used to establish system settings |
|
|
Visual Basic® files (VBE and VBS) Used to script in visual basic which is built into many Windows-based machines |
|
|
Windows Script Host Settings File Used to configure the script interpreter program on Windows machines |
Official (ISC)²® Guide to the SSCP® CBK®
By Diana-Lynn Contesti, Douglas Andre, Eric Waxvik, Paul A. Henry, Bonnie A. Goins
Published by (ISC)2 Press
ISBN # 9780849327742; Copyright 2007; Pages: 573; Edition: 1st
Chapter: Domain 7:
Malicious Code
By Diana-Lynn Contesti, CISSP-ISSAP, ISSMP, SSCP
This was first published in August 2007
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