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Configuring Blocked File Extensions

Archived content. No warranty is made as to technical accuracy. Content may contain URLs that were valid when originally published, but now link to sites or pages that no longer exist.

Microsoft provides the ability to restrict certain kinds of files from being uploaded or retrieved, based on the file extension. For example, a file with the .exe file extension could potentially contain code that runs on client computers when it is downloaded. Because it has the .exe file extension, the file can be run on demand when it is downloaded. If files with the .exe file extension are blocked, users can neither upload nor download a file with the .exe extension, and potentially dangerous content in the .exe file cannot be downloaded. This feature does not prevent all exploits based on file types, nor is it designed to do so.

By default, several standard file extensions are blocked, including any file extensions that are treated as executable files by Windows Explorer. Files with curly braces { or } are also blocked automatically. The file extensions blocked by default are:

File extension

File type

.ade

Microsoft Access project extension

.adp

Microsoft Access project

.app

Application file

.bas

Microsoft Visual Basic class module

.bat

Batch file

.chm

Compiled HTML Help file

.class

Java class file

.cmd

Microsoft Windows NT Command Script

.com

Microsoft MS-DOS program

.cpl

Control Panel extension

.crt

Security certificate

.dll

Windows dynamic link library

.exe

Excutable program

.fxp

Microsoft Visual FoxPro compiled program

.hlp

Help file

.hta

HTML application

.ins

Internet Naming Service

.isp

Internet Communication settings

.jse

JScript Encoded Script file

.lnk

Shortcut

.mda

Microsoft Access add-in program

.mdb

Microsoft Access program

.mde

Microsoft Access MDE database

.mdt

Microsoft Access data file

.mdw

Microsoft Access workgroup

.mdz

Microsoft Access wizard program

.msc

Microsoft Common Console Document

.msi

Microsoft Windows Installer package

.msp

Windows Installer update

.mst

Visual Test source files

.ops

Microsoft Office profile settings file

.pcd

Photo CD image or Microsoft Visual Test compiled script

.pif

Shortcut to MS-DOS program

.prf

System file

.prg

Program source file

.reg

Registration entries

.scf

Windows Explorer command file

.scr

Screen saver

.sct

Windows Script Component

.shb

Windows shortcut

.shs

Shell Scrap Object

.url

Uniform Resource Locator (Internet shortcut)

.vb

Visual Basic Scripting Edition (VBScript)file

.vbe

VBScript Encoded Script file

.vbs

VBScript file

.wsc

Windows Script Component

.wsf

Windows Script file

.wsh

Windows Script Host Settings file

The list of file extensions is controlled for the entire server or server farm and is recorded in the configuration database. Because the list of blocked file types is maintained by file extension, all files that use a file extension on the list cannot be uploaded or downloaded, irrespective of the file's intended use. If .asp is on the list of extensions to block, the feature blocks all .asp files on the server, even if they're used to support Web site features on another server in the server farm. If a file ends in a period (.), the preceding characters are checked against the list of blocked file extensions as well. For example, if .exe is on the list of blocked file extensions, a file called "filename.exe." is also blocked. The following list shows different ways of representing the same file, all of which are blocked if the .hta extension is on the list of blocked file extensions:

  • filename.hta

  • filename.hta.

  • filename.hta.{3050F4D8-98B5-11CF-BB82-00AA00BDCE0B}

  • filename.hta::$DATA

You can determine which files are blocked for Web sites on your servers by modifying the list of blocked file extensions. You can block additional file extensions (up to 1024 file types) by adding them to the list in the SharePoint Central Administration pages, or remove a block by deleting the file extension from the list. When you change the list of file extensions, the change affects both new files being added to a Web site and files already posted to a Web site. For example, if a document library contains a .doc file, and you add the .doc file extension to the list of blocked file extensions, users will no longer be able to open the .doc file in the document library. Users will be able to rename or delete a file with a blocked file extension, but will not be able to perform any other actions.

Add or remove a file type from the list of blocked file extensions

  1. Click Start , point to All Programs , point to Administrative Tools , and then click SharePoint Central Administration .

  2. On the SharePoint Central Administration page, under Security Configuration , click Manage blocked file types .

  3. On the Manage List of Blocked File Types page, perform one of the following actions:

    • To add a file type, click in the list and type the extension.

    • To delete a file type, delete the file extension from the list.

  4. Click OK .

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