List of blocked file extensions

Copyright © 2021-2022 ZOBEC Consulting. All Rights Reserved.

About this repository

This repository contains list of unwanted or suspicious file extensions in Windows environment. You can use in for example Microsoft OneDrive, Microsoft SharePoint, or Microsoft Exchange.

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The background of the creation of this repository

During implementation of OneDrive and SharePoint, I wanted to implement blocking of unwanted or suspicious file extensions. I make list of blocked type of files and after finish I got think publish him on my web.

In time I had to make some extensions of this list, because list is still not perfect and some file extensions will be good to add to block list. But in this phase I had problem, because actual list it was only as article on my web, but in SharePoint you must enter list of extensions as plain text list, with one file extension in one row. And tracking of changes it was too complicated.

So I moved this list to this repository, where I can better and more easy track of any change.

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Table with blocked file extensions

File type	Extension	Reson for blocking
Application files in Windows	com exe dll ocx	Potentially dangerous. Unwanted to save on OneDrive.
PowerShell script files	ps1 ps1xml ps2 ps2xml psc1 psc2 msh msh1 msh2 mshxml msh1xml msh2xml	Potentially dangerous. Unwanted to save on OneDrive.
Windows JavaScript files	js jse	Potentially dangerous. Unwanted to save on OneDrive.
Windows Visual Basic Script files	vbs vb vbe	Potentially dangerous. Unwanted to save on OneDrive.
Windows Commandline script files	cmd bat	Potentially dangerous. Unwanted to save on OneDrive.
HTML Application (Internet Explorer)	hta	Potentially dangerous. Unwanted to save on OneDrive.
Windows Installation file	inf	Potentially dangerous. Unwanted to save on OneDrive.
Windows Registry configuration file	reg	Potentially dangerous. Unwanted to save on OneDrive.
MS-DOS configuration link	pif	Potentially dangerous. Unwanted to save on OneDrive.
Windows Screensaver file	scr	Potentially dangerous. Unwanted to save on OneDrive.
Windows Control Panel applet file	cpl	Potentially dangerous. Unwanted to save on OneDrive.
Windows Explorer command file	scf	Potentially dangerous. Unwanted to save on OneDrive.
Microsoft Management Console file	msc	Potentially dangerous. Unwanted to save on OneDrive.
Windows Group Policy file	pol	Potentially dangerous. Unwanted to save on OneDrive.
Windows Help files	hlp chm	Potentially dangerous. Unwanted to save on OneDrive.
Windows Host Script files	ws wsf wsc wsh	Potentially dangerous. Unwanted to save on OneDrive.
Java archive / Java class file	jar	Potentially dangerous. Unwanted to save on OneDrive.
Various file archive file types	rar z bz2 cab gz tar ace	Unused (compressed) archive file types. Allowed file types is only ZIP and 7z (7-Zip). Other file types are not used to ensure compatibility and unification of archive file types used.
Windows Installer files	msi msp mst	No any reason for save on OneDrive.
Windows Update files	msu	No any reason for save on OneDrive.
Windows Provisioning Package file	ppkg	Potentially dangerous. Unwanted to save on OneDrive.
SQL Server backup file	bak	No any reason for save on OneDrive.
Temporary files	tmp	It can create many write operations and overload OneDrive and Internet line unnecessarily. No any reason for save on OneDrive.
Outlook offline file	ost	No any reason for save on OneDrive.
Outlook data file	pst	No any reason for save on OneDrive.
Apple macOS installation file	pkg	No any reason for save on OneDrive.
ISO Image files	iso img	File with image of the CD/DVD media. A potentially large file in the order of tens of GB. Unwanted to save on OneDrive.
Hyper-V Virtual Hard Disk files	vhd vhdx	It can create many write operations and overload OneDrive and Internet line unnecessarily. No any reason for save on OneDrive.
ClickOnce Deployment file	application	Potentially dangerous. Unwanted to save on OneDrive.
Universal lock extension file	lock lck	Lock file used by various applications. It is undesirable to use OneDrive as storage for running applications. It can create many write operations and overload OneDrive and Internet line unnecessarily. No any reason for save on OneDrive.
C# source code files	sln cs csproj resx config resources pdb manifest	It is not desirable to store source codes on OneDrive. Source code repositories such as GitHub or Azure DevOps are used for this purpose. No any reason for save on OneDrive.
Audio file	mp3 wma	Possible source of copyright issues. Unwanted to save on OneDrive.
Microsoft Office Word legacy file format	doc dot wbk	Unwanted to save on OneDrive.
Microsoft Office Excel legacy file format	xls xlt xlm xla	Unwanted to save on OneDrive.
Microsoft Office PowerPoint legacy file format	ppt pot pps	Unwanted to save on OneDrive.
Microsoft Office Access legacy file format	ade adp mdb cdb mda mdn mdt mdf mde ldb	Unwanted to save on OneDrive.
Microsoft Works file format	wps	Unwanted to save on OneDrive.
Microsoft Office Excel Add-in files	xlsb xlam xll xlw	Potentially dangerous. Unwanted to save on OneDrive.
Microsoft PowerPoint Add-in file	ppam	Unwanted to save on OneDrive.

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Documentation (all documents)

• Main document (ReadMe).
• List of blocked files in plain text file.
• History.
• License.

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Links

• Microsoft 365/Office 365: OneDrive: Zakázané typy souborů (blocked file types) na OneDrive
• SwiftFilter/Audit-ExternalSuspiciousAttachments.txt
• Awesome Windows Domain Hardening
• CryptoBlocker - A script to deploy File Server Resource Manager and associated scripts to block infected users
• Anti-Ransomware File System Resource Manager Lists - API: Get file list