File types and extensions in email attachments that are common threat vectors

Products

• Mail Security for Microsoft Exchange
• Email Security.cloud
• Messaging Gateway

Issue/Introduction

 File types and extensions that are common threat vectors in email attachments.

Resolution

File attachments in email are common threat vectors for malware. Executable files are not the only file type that can include threats. For example, Microsoft Office documents (e.g. doc, docx, xlx, xlsx, ppt, pptx, etc) can contain macros or scripts that include threats.

Blocking specific file extensions or types can limit exposure to risk.

CAUTION:

• Blocking files extensions does not remove all risk of malicious files being received.
• Blocking file extensions can also block valid files.

Most Symantec Mail Security products have the ability to block attachments by file extension. Some products can also block the true file type, even if the file has been renamed (e.g. foo.exe to foo.txt).

Check your Symantec product documentation to see which file blocking or content filtering options are available.

Note: In cases where users still need to share blocked file types, set up alternative methods to transfer or share these files.

Table: File extensions and types

File Extension	File Type
.adp	Access Project (Microsoft)
.app	Executable Application
.asp	Active Server Page
.bas	BASIC Source Code
.bat	Batch Processing
.cer	Internet Security Certificate File
.chm	Compiled HTML Help
.cmd	DOS CP/M Command File, Command File for Windows NT
.cnt	Help file index
.com	Command
.cpl	Windows Control Panel Extension (Microsoft)
.crt	Certificate File
.csh	csh Script
.der	DER Encoded X509 Certificate File
.exe	Executable File
.fxp	FoxPro Compiled Source (Microsoft)
.gadget	Windows Vista gadget
.hlp	Windows Help File
.hpj	Project file used to create Windows Help File
.hta	Hypertext Application
.inf	Information or Setup File
.ins	IIS Internet Communications Settings (Microsoft)
.isp	IIS Internet Service Provider Settings (Microsoft)
.its	Internet Document Set, Internet Translation
.js	JavaScript Source Code
.jse	JScript Encoded Script File
.ksh	UNIX Shell Script
.lnk	Windows Shortcut File
.mad	Access Module Shortcut (Microsoft)
.maf	Access (Microsoft)
.mag	Access Diagram Shortcut (Microsoft)
.mam	Access Macro Shortcut (Microsoft)
.maq	Access Query Shortcut (Microsoft)
.mar	Access Report Shortcut (Microsoft)
.mas	Access Stored Procedures (Microsoft)
.mat	Access Table Shortcut (Microsoft)
.mau	Media Attachment Unit
.mav	Access View Shortcut (Microsoft)
.maw	Access Data Access Page (Microsoft)
.mda	Access Add-in (Microsoft), MDA Access 2 Workgroup (Microsoft)
.mdb	Access Application (Microsoft), MDB Access Database (Microsoft)
.mde	Access MDE Database File (Microsoft)
.mdt	Access Add-in Data (Microsoft)
.mdw	Access Workgroup Information (Microsoft)
.mdz	Access Wizard Template (Microsoft)
.msc	Microsoft Management Console Snap-in Control File (Microsoft)
.msh	Microsoft Shell
.msh1	Microsoft Shell
.msh2	Microsoft Shell
.mshxml	Microsoft Shell
.msh1xml	Microsoft Shell
.msh2xml	Microsoft Shell
.msi	Windows Installer File (Microsoft)
.msp	Windows Installer Update
.mst	Windows SDK Setup Transform Script
.ops	Office Profile Settings File
.osd	Application virtualized with Microsoft SoftGrid Sequencer
.pcd	Visual Test (Microsoft)
.pif	Windows Program Information File (Microsoft)
.plg	Developer Studio Build Log
.prf	Windows System File
.prg	Program File
.pst	MS Exchange Address Book File, Outlook Personal Folder File (Microsoft)
.reg	Registration Information/Key for W95/98, Registry Data File
.scf	Windows Explorer Command
.scr	Windows Screen Saver
.sct	Windows Script Component, Foxpro Screen (Microsoft)
.shb	Windows Shortcut into a Document
.shs	Shell Scrap Object File
.ps1	Windows PowerShell
.ps1xml	Windows PowerShell
.ps2	Windows PowerShell
.ps2xml	Windows PowerShell
.psc1	Windows PowerShell
.psc2	Windows PowerShell
.tmp	Temporary File/Folder
.url	Internet Location
.vb	VBScript File or Any VisualBasic Source
.vbe	VBScript Encoded Script File
.vbp	Visual Basic project file
.vbs	VBScript Script File, Visual Basic for Applications Script
.vsmacros	Visual Studio .NET Binary-based Macro Project (Microsoft)
.vsw	Visio Workspace File (Microsoft)
.ws	Windows Script File
.wsc	Windows Script Component
.wsf	Windows Script File
.wsh	Windows Script Host Settings File
.xnk	Exchange Public Folder Shortcut
.ade	ADC Audio File
.cla	Java class File
.class	Java class File
.grp	Microsoft Widows Program Group
.jar	Compressed archive file package for Java classes and data
.mcf	MMS Composer File
.ocx	ActiveX Control file
.pl	Perl script language source code
.xbap	Silverlight Application Package

Note: This list is by no means exhaustive. It is up to your discretion as an administrator which items to block.