Microsoft Defender Application Guard for Office (2023)


This is JohnBarbareand I am a SrCustomerEngineer at Microsoft focusing on all things in the Cybersecurity space. In thisblogI willfocus onMicrosoft DefenderApplication Guardfor Officeavailable generally available (as of 01/28/21) for all E5 customers.For the last several months I havetested and demoedmultiple new features inWindows10 20H1as I wasonMicrosoft’s Elite Program before itbecame available in Public Preview.Onecan access the latest KB4571756 (OS Build 19041.508) for the installation instructions for any admins which are ready without a need for policy package download by following the details here.

My interest inMicrosoft Defender Application Guardcame fromdemoing and thendeploying to several large clientslast yeardue to a high interest of attackersdeveloping new techniquestobreachlarge scalenetworksandcompromisingworkstations. Withphishing schemesremainingone of the top ways todupeusersinto social engineering attacks,Microsoft Defender Application Guardis engineered anddesigned to proactively prevent multiple types of attacks.When Microsoft extendedMicrosoft Defender Application Guardfor Office,itfurther decreased the overall attack surface reductionwhilealso increasingemployee’sproductivity.Before we go into the featuresofMicrosoft Defender Application Guardfor Office, I will go over a brief introduction toMicrosoft Defender Application Guardif one is not familiar.

Update - 02/01/2021 - Changed public preview to generally available as of 01/28/21 with reference to the article here.

Prerequisites forMicrosoft Defender Application Guard

Hardware Requirements

  • A 64-bit computer witha minimum of4 cores (logical processors) isrequiredfor hypervisor and virtualization-based security (VBS). For more info about Hyper-V,seeHyper-V on Windows Server 2016/2019 or Introduction to Hyper-V on Windows 10. For more info abouthypervisors,seeHypervisor Specifications
  • CPUvirtualization extensions-Extended page tables, also called Second Level Address Translation (SLAT)and one of the following virtualization extensions forVBS:VT-x (Intel)orAMD-V
  • Minimum8GB RAM
  • 5GBfree space, solid state disk (SSD) recommended for hard diskspace

Software requirements

  • Operatingsystem -Windows 10 Enterprise edition, version 1709 or higher
    Windows 10 Professional edition, version 1803 or higher
    Windows 10 Professional for Workstations edition, version 1803 or higher
    Windows 10 Professional Education edition version 1803 or higher
    Windows 10 Education edition, version 1903 or higher
  • Browser– Any variant ofMicrosoft Edge and Internet Explorer

Microsoft Defender Application GuardBrief Overview

Microsoft DefenderMicrosoft Defender Application Guardis a hardware Isolationleveraginga Hyper-V enabledcontainer.The container uses a lightweightVirtual Machine (VM)that is resistant tokernelattacksand runsona separatekernelfrom the host.There are two types of modes-EnterpriseManagement Mode andStandalone Mode. In EnterpriseManagement Mode, theadministrator defines trusted sites throughGPOs,Microsoft Intune, Microsoft Endpoint ConfigurationManager,or your current mobile device managementsolution. Untrusted sites launch in the isolated Hyper-V containergiving the user amalicious free browsing session.

MicrosoftDefenderApplication Guardwascreated to targetthe followingtypes of systems:

  • Enterprise Desktops and Laptops-Domain-joined and managed by your organization.
  • Bring your own device- Personally-owned laptops are not domain-joined, but are managed by your organization through tools, such as Microsoft Intune.
  • Personal devices- Personally-owned desktops or mobile laptops are not domain-joined or managed by an organization. The user is an admin on the device and uses a high-bandwidth wireless personal network while at home or a comparable public network while outside.

In StandaloneMode, users can use hardware-isolatedbrowsing sessions without any administrator or management policy configuration. In this mode, you must installMicrosoft Defender Application Guardand then the user must manually startMicrosoft Defender Application Guardwhile browsing trusted/untrusted sites.I normallydo notrecommend Standalone Modeto clients as it lets the userdecideif they want to useaMicrosoft Defender Application Guardsession ortonotuse. Thenthe user canallow any action (good or bad)which might result inmaliciousbehavior.

The following is adiagramof controls that areconfigurable forMicrosoft Defender Application Guardsessions:

(Video) Microsoft 365 Webinar: Introduction to Microsoft Defender Application Guard for Office

Microsoft Defender Application Guard for Office (1)AppGuard Policies

If an employee goes to an untrusted site, Microsoft Edge opens the site in an isolated Hyper-V-enabled container, which is separate from the host operating system. This container isolation means that if the untrusted site turns out to be malicious, the hostPCisprotectedand the attackercannotbreak out of the containerorgain access to the local machine.The container is left running and until sign off orrebootsthe container is running in the background.For example, this approach makes the isolated container anonymous, so an attackercannotget to your employee's enterprise credentialsor other sensitive information.Capabilities have also been extended forApplicationGuard forGoogle ChromeandMozilla Firefoxwith browser side extensionsas of this publicationfor users that chose other browsers.

Microsoft Defender Application Guardfor Office

Asstatedpreviously, multiple files, phishing attacks, and malicious contentfrom the internetpose a threat to users. Various other attack vectors,whichincludepotentially unsafe locations,cancontainviruses, worms, or other kinds of malware that can harm your computer and/orsensitivedata.Microsoft Defender Application Guardsteps in and gives you a second barrier tohelp protect youagainst these attacks.MicrosoftOfficewillopen files from potentially unsafe locations in  Microsoft Defender Application Guard, a secure container,that isisolated from the device through hardware-based virtualization. WhenMicrosoftOffice opens files inMicrosoft Defender Application Guard,a usercanthensecurely read, edit,  print, and save thefiles without having to re-open files outsideofthe container.

Below are theprerequisites for Microsoft Defender Application Guard for Office:

Minimum hardware requirements

  • CPU: 64-bit, 4 cores (physical or virtual), virtualization extensions (Intel VT-x OR AMD-V), Core i5 equivalent or higher recommended
  • Physical memory: 8-GB RAM
  • Hard disk: 10 GB of free space on the system drive (SSD recommended)

Minimum software requirements

  • Windows 10: Windows 10 Enterprise edition, Client Build version 2004 (20H1) build 19041
  • Office: Office Beta Channel Build version 2008 16.0.13212 or later
  • Update package: Windows 10 cumulative monthly security updates KB4566782

The settings forMicrosoft Defender Application Guardfor Office haveadditionalcontrols you can set asdepictedbelow.Office files supported includeExcel for Microsoft 365,Word for Microsoft 365, andPowerPoint for Microsoft 365.

Microsoft Defender Application Guard for Office (2)AppGuard Policies for Office

Depending onif youset your configurations for the user to change the settings after opening the fileor if you block the user with no privileges, onecan see the difference in each Office file asseen in the image below.

Microsoft Defender Application Guard for Office (3)Different views per setting

If your administrator has enabled Safe Documents, the file will be verified againsttheMicrosoft Defender Advanced Threat Protection service todetermineifit ismalicious beforeit isopened outsideMicrosoft Defender Application Guard.

Officewill automatically useMicrosoftDefender Application Guardto isolate untrusted documents under the following conditions:

  • Microsoft Defender Application Guardis enabled in Windows. This can be enabled by either an administrator deploying policy or the user.
  • The user is usingMicrosoft365 Apps for enterpriseclient.
  • The user signedintoOffice is licensed forMicrosoft Defender Application Guard.Microsoft Defender Application Guardfor Office will require either a Microsoft 365 E5 or Microsoft 365 E5 Security license.

If any of these conditionsarenot met, Office will use Protected View to isolate untrusted documents.

(Video) Introduction to Microsoft Defender Application Guard for Office -Microsoft 365 Webinar

Filesthat arecurrently open in Protected View will open inMicrosoft Defender Application Guard. These include:

  • Files originating from the internet: This refers to files that are downloaded from domains thatare notpart of either the local intranet or a Trusted Sites domain on your device.
  • Files thatare located inpotentially unsafe locations: This refers to folders on your computer or network that are considered unsafe, such as the Temporary Internet folder or other folders assigned by your administrator.
  • Outlook attachments: Attachments in email can come from unreliable or unknown sources, such as someone outside your organization. Sometimes malicious attachments can appear to come from trusted senders or compromised accounts of trusted senders. Always confirm with the sender if you receive an unexpected or suspicious attachment via email.

Walkthrough of OpeninganOffice Filein Microsoft Defender Application Guard

Illdemousing Microsoft Edge Chromium inUserModeon my test machineto showhowMicrosoft Defender Application GuardforOffice will openan Officefile.The settings will be slightly different as it will give me more optionsto choosefrom,which might be risky in some environmentscompared to Enterprise Mode.

Iwill firstdo a quick search for “Clemson TigersFootballResume Template” on andlocatethe website thatcontainsthe Office fileI need. Ifindthe site thatcontainsthe file,but as a regular user,I am not sure if the site(or file)hasbeen spoofed,containsmalicious content, or an active Ransomware campaignis in theOfficefile that will lock all the files on my computer.I go ahead and click theURLtoopenthe Office fileknowing I will be protected withMicrosoft Defender Application Guardfor Office.

Microsoft Defender Application Guard for Office (4)Searching for an untrusted Office document to open

When the file opens, it automatically goes into a container inMicrosoft Defender Application Guardfor Officeas you can see from the window below.

Microsoft Defender Application Guard for Office (5)Untrusted Office document opening in AppGuard for Office

Once the file is open on my machine, I canview the document and the icon for Word on thetaskbarhas theshield inside to show that I amprotected by usingMicrosoft Defender Application Guardfor Office.

Microsoft Defender Application Guard for Office (6)Word document in the container

In addition to being able to readthedocumentwithin the secure container,onecan now use features like printing, commenting and review, light editing, and saving, while keepingtheuntrusted document within theMicrosoft Defender Application Guardcontainer. 

When youencounterdocuments from untrusted sources thatare notmalicious, you can continue to be productive without worrying about putting your device at risk.If you doencountera documentthat ismalicious,it issafely isolated withinMicrosoft Defender Application Guard, keeping the rest of your systems safe.

Afterfinishingthe template, I will go ahead and save on my local machine and theOffice file will still be saved in an isolated container.The reason I saved on my local machine is because while the Office file is in the container, a user is not allowed to choose OneDrive in Office Backstage. When one opens a file which is saved "as is" on a local machine, one can choose the sync'd location from OneDrive (documents from OneDrive and OneDrive for business will not open in a container). I have my settings configuredso I cantake it out of the containerif Itrust the source on my local machine. For testing purposes, I have it configured like this to show you the different options. Always test allMicrosoft Defender Application GuardOffice settings in a testenvironmentbefore implementing in production.

Microsoft Defender Application Guard for Office (7)AppGuard save as local folder on machine

Next,I will go into my local saved folderandclick on thesameOffice file. Noticeitwill open again inMicrosoft Defender Application Guardfor Office.

(Video) Hardware Isolated Browsing w/ Microsoft Defender Application Guard

Microsoft Defender Application Guard for Office (8)Opening back up the Office file

Once the file opens, you can see theWord documentopens back upinMicrosoft Defender Application Guardfor Officeas seen in thecalled-outboxes.

Microsoft Defender Application Guard for Office (9)Office document opening back up in container

If I want to save the file outside the container, I can do so in this modealso.Once I clickon the"Remove Protection”,the file is automatically scanned for any types of malicious threats orembedded scripts in Microsoft DefenderATP.It is very important that SafeDocs is enabled so it will be triggered and scanned by Microsoft Defender ATP.

Microsoft Defender Application Guard for Office (10)Removing protection

The file being scanned by Microsoft Defender ATP to bedeemedsafe before being saved locally.

Microsoft Defender Application Guard for Office (11)Office file being scanned for threats

As one cansee,the file has beendeemedsafe andthe file will be savedinthe folder of yourchoicewith thenecessarypermissions.

Testing a Malicious (test) Word Document

To see what a malicious word document will do when trying to take it out of the container,we will download a testWorddocumentthatwill createmaliciousexecutable contentthough an embedded macro.If your enterprise allows unsigned macros and they happen to be malicious, you will see what happens next.You can download the safe test file from Microsoft’s Attack Surface ReductionRules test sitelocatedhere. Once we click on the link and open the file, it automatically opens inMicrosoftDefenderApplication Guard for Office.

Microsoft Defender Application Guard for Office (12)Opening a malicious Office file

When we go to save the file andattempt totake it out of the container (removing the protection),we are prompted with the following screen. I will go ahead and click onremove protectionto see the actions that are taken.

Microsoft Defender Application Guard for Office (13)Removing protection

The file isconfirmedto remove the protectionand thenscanned.

(Video) Application Guard for Office & Safe Documents in action !

Microsoft Defender Application Guard for Office (14)Removing protection confirmation

Microsoft Defender Application Guard for Office (15)Office file being scanned for threats

The file is openedoutside the containerwith asecurity warning:macroshave beendisabledasithasbeendetermined to havea malicious macro(s)inside the Office document. Once I click onenablecontent to enable the macro(s), I am further prevented from working or editing the file.

Microsoft Defender Application Guard for Office (16)Security warning that macros have been disabled due to a threat

The fileshows me the warning with information about the macro(s) and the Office filewill be automatically closed and be prevented from running the malicious content.

Microsoft Defender Application Guard for Office (17)Confirmation of the threat and Office file closing


Thanks for taking the time to read thisblogand I hope you had fun readingabout the newMicrosoft Defender Application Guardfor Office.Since Office documents areimmensely popularvectors for attacks, this new security featurewillassistyour enterprise in stoppingOffice fileattacksby keeping themcontained. By having thisenhanced security feature, it will increase user productivityacross your enterprise.Alwaystestand refine these settings with a pilot group of users and devices first,before widelydistributingto your organization!This new feature bringstogetherOffice, Windows, and Microsoft Defender ATPfor an integrated value.

Hope to see you inmynextblogand always protect your endpoints!

Thanks for reading and have a great Cybersecurity day!

Follow my MicrosoftSecurity Blogs:  andalsoonLinkedIn.


Application Guard for Office

Application Guard for Office for Admins

(Video) Defrag Tools #196 - Windows Defender Application Guard

How to Enable SafeDocs

Microsoft Defender Application Guard Overview


What is Microsoft Defender application Guard? ›

Microsoft Defender Application Guard (Application Guard) is designed to help prevent old and newly emerging attacks to help keep employees productive. Using our unique hardware isolation approach, our goal is to destroy the playbook that attackers use by making current attack methods obsolete.

Should I enable Microsoft Defender application Guard? ›

Designed to protect your security, it generally shouldn't be trifled with, but you may want to turn it on or off on your personal PC. Windows Defender Application Guard and its enforcer, Windows Defender Application Control, are tools to keep employees productive and prevent attacks.

What is Microsoft application guard for Office 365? ›

Application Guard for Office is a protected mode that isolates untrusted documents so that they can't access trusted corporate resources, an intranet, the user's identity, and arbitrary files on the computer.

How do I turn off application Guard in Word? ›

To remove Application Guard protection go to File > Info and select Remove protection. If you're unable to, then it's likely that your organization has policies deployed that prevent removing Application Guard protection from a file.

Do I need application Guard? ›

If you want to protect your computer from online attacks more, you should also use Application Guard, and here's how on Windows 11. On Windows 11, the "Microsoft Defender Application Guard" feature lets you browse untrusted websites securely using Microsoft Edge.

Does Microsoft Defender application Guard work with Chrome? ›

Microsoft Defender Application Guard Extension is a web browser add-on available for Chrome and Firefox.


1. Preventing browser-based attacks with Windows Defender Application Guard
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2. How To Configure Defender Application Guard using Microsoft Endpoint Manager
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3. Microsoft Defender Application Control
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4. Configure Microsoft Defender Application Guard using Microsoft Intune
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5. Ignite | September 2020 | Browser Isolation using Application Guard
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6. Windows 10: How to activate Microsoft Defender Application Guard
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