IIS_IUSRS and IUSR permissions in IIS8

Question

I've just moved away from IIS6 on Win2003 to IIS8 on Win2012 for hosting ASP.NET applications.

Within one particular folder in my application I need to Create & Delete files. After copying the files to the new server, I kept seeing the following errors when I tried to delete files:

Access to the path 'D:\WebSites\myapp.co.uk\companydata\filename.pdf' is denied.

When I check IIS I see that the application is running under the DefaultAppPool account, however, I never set up Windows permissions on this folder to include IIS AppPool\DefaultAppPool

Instead, to stop screaming customers I granted the following permissions on the folder:

IUSR

• Read & Execute
• List Folder Contents
• Read
• Write

IIS_IUSRS

• Modify
• Read & Execute
• List Folder Contents
• Read
• Write

This seems to have worked, but I am concerned that too many privileges have been set. I've read conflicting information online about whether IUSR is actually needed at all here. Can anyone clarify which users/permissions would suffice to Create and Delete documents on this folder please? Also, is IUSR part of the IIS_IUSRS group?

Swerve

To get WordPress working on IIS 8 on an Azure virtual machine (Windows Server 2012 Datacenter) I needed to grant the permissions you have listed for IIS_IUSRS to IUSR for the blog directory in inetpub/wwwroot – Hemelytron

For those who come to this thread because they're trying to run Joomla under IIS and are having problems with the file security settings, I've written a blog article with what I think is the proper solution. Probably also applicable to WordPress or other PHP-based web server programs. renniestechblog.com/index.php/information/… – Sonnysonobuoy

Possible duplicate of IIS AppPoolIdentity and file system write access permissions – Mattson

Working fine after adding full permission for folder for user group IIS_IUSRS. – Latty

@Latty but then you've given full privileges to all IIS Users. Think about that from a hacker's perspective. One weak site and they gain total control of all the rest – Swerve

@Swerve Thanks for Information we are changing the permission now... :) – Latty

Answer 1

I hate to post my own answer, but some answers recently have ignored the solution I posted in my own question, suggesting approaches that are nothing short of foolhardy.

In short - you do not need to edit any Windows user account privileges at all. Doing so only introduces risk. The process is entirely managed in IIS using inherited privileges.

Applying Modify/Write Permissions to the Correct User Account

1. Right-click the domain when it appears under the Sites list, and choose Edit Permissions

Under the Security tab, you will see MACHINE_NAME\IIS_IUSRS is listed. This means that IIS automatically has read-only permission on the directory (e.g. to run ASP.Net in the site). You do not need to edit this entry.

2. Click the Edit button, then Add...

3. In the text box, type IIS AppPool\MyApplicationPoolName, substituting MyApplicationPoolName with your domain name or whatever application pool is accessing your site, e.g. IIS AppPool\mydomain.com

4. Press the Check Names button. The text you typed will transform (notice the underline):

5. Press OK to add the user

6. With the new user (your domain) selected, now you can safely provide any Modify or Write permissions

Swerve

This did not work on my IIS 8.5 server. Adding IUSR works. Adding IIS AppPool\Cache (the name of my application pool) yields HTTP Error 401.3 - Unauthorized – Twomey

@CharlesBurns I had the same issue, I found this to be my root cause: techras.wordpress.com/2016/03/09/… (anonymous auth was set to use IUSR instead of Application Pool Identity) – Tann

I had a folder used only as a Virtual Directory and it worked fine up until I shared it (the windows folder it pointed to) with another domain account, so it could view the files over our intranet. When I did this, the files in the Virtual Directory suddenly became unreachable. I ended up having to add both MyComputerName\IIS_IUSRS and IUSR with Read only permissions for it to work again. This is just for Virtual Directories (not .net Apps), but figure someone may find it useful. – Chaste

Just a note: When you search for the user and the computer is a member of a domain, the IIS AppPool\MyApplicationPoolName may not be found. In my case, I needed to click the Locations button and change the location to the local computer. – Lippi

Can confirm, statler is correct; when operating on a domain, you must change the location to be the local machine first. – Aerodontia

In my tests the name of the special user to use here has nothing to do with a domain name. It is the name of the Application Pool that is assigned to the site in IIS. This Application Pool may or may not have a name that matches the domain of your website. So the pattern is: IIS AppPool\[APPLICATION POOL NAME]. Blanks in the Application Pool name are accepted. Please also note that this user will only be found, if "Built-in security principals" is checked as an object type for the name search (top field in the "Select Users or Groups" dialog). – Knut

Hi. I tried your solution but when I try to add IIS App Pool\App pool name gives me this : An object named "IIS AppPool\Default Web Site" cannot be found. Check the selected object types and location for accuracy and ensure that you typed the object name correctly, or remove this object from the selection. I replicated each step as mentioned in your answer , but still it wont work? – Slapstick

You could also add a comment about the AppPoolIdentity being set as the Identity for the corresponding application pool (for that domain). – Cystocele

So IUSR (anonymous user) is used by IIS to access the contents of the folder where as the IIS AppPool\AppPoolName user is used by IIS to run the code? – Tangy

Answer 2

IUSR is part of the IIS_IUSER group, so I guess you can remove the permissions for IUSR without worrying. Further reading

However, a problem arose over time as more and more Windows system services started to run as NETWORKSERVICE. This is because services running as NETWORKSERVICE can tamper with other services that run under the same identity. Because IIS worker processes run third-party code by default (Classic ASP, ASP.NET, PHP code), it was time to isolate IIS worker processes from other Windows system services and run IIS worker processes under unique identities.

The Windows operating system provides a feature called "Virtual Accounts" that allows IIS to create unique identities for each of its Application Pools. DefaultAppPool is the default pool that is assigned to all Application Pools you create.

To make it more secure you can change the IIS DefaultAppPool Identity to ApplicationPoolIdentity.

Regarding permissions, Create and Delete summarize all the rights that can be given. So whatever you have assigned to the IIS_USERS group is all that they will require.

Pulmonate

I just installed IIS 8 under Server Essentials 2012 R2. This machine is also a domain controller. In AD Users and Computers, the IIS_IUSRS group is empty--it does not contain the IUSR user. I suppose I could add it to the group, but for anonymous sites, I'll just grant permissions to the IUSR user. – Radiophone

When I granted permissions for IUSR it worked. When I granted permissions to IIS_IUSER it did not work. – Impasse

Iusr is not a member of IIS_Iusrs. (or windows have a bug) Generally, Windows uses IIS_Iusrs. (executing dynamic pages or accessing static pages) but there is some cases when windows uses Iusr, not IIS_Iusrs. file upload using PHP is one of that case. (and if you granted iis_iusr only, you will meet privilege exception) I think M$ should give "A best-practice" for granting permssion of Iusr and IIS_Iusrs... – Mclemore

I think now its changed to Application pool group i.e (IWGP) . I gave permissions to IWGP and it worked . – Norvun

IUSR is part of IIS_IUSER. NO IT IS NOT! IUSR is the anonimous user, IIS_IUSER is the group for apppool users – Revenge

Answer 3

When I added permissions for IIS_IUSRS to the site folder, resources like JavaScript and CSS were still inaccessible (error 401, forbidden). However, when I added IUSR, it started working. So for sure you cannot remove the permissions for IUSR.

Neoclassicism

Don't forget that (if you have IIS7+) the correct solution is to use IIS AppPool\MyApplicationPoolName as per my updated answer. You don't need to mess about with IUSR(S) any more! – Swerve

I've tried your suggestion, but it does not work. I have removed IUSR(S) from permission and remained only the poolname, app is running under. Resources became unaccessible. IIS 8.5. When I added IUSR - it got working. – Neoclassicism

You need to post your own question with as much information about your situation please. – Swerve

@EvilDRr dotNet code will run as the application pool user (if that's what the identity of the appPool has been configured to use). Otherwise, anonymous requests to (static) resources such as images will be handled via the anonymous authentication of which IUSR is the default identity. – Chirrupy

Answer 4

@EvilDr You can create an IUSR_[identifier] account within your AD environment and let the particular application pool run under that IUSR_[identifier] account:

"Application pool" > "Advanced Settings" > "Identity" > "Custom account"

Set your website to "Applicaton user (pass-through authentication)" and not "Specific user", in the Advanced Settings.

Now give that IUSR_[identifier] the appropriate NTFS permissions on files and folders, for example: modify on companydata.

Pander

Thanks but I'm not using AD. Also according to recent MS documentation, IIS 7&8 are already configured to work as you describe. The question really is whether one of the specified accounts is actually needed or not, and which one does the business? – Swerve

@Swerve Thanks for clarifying you are not using an AD. Well, IIS_IUSRS is not a user, it's a group. Like IIS_WPG on IIS 6.0. You can read about IIS_IUSRS and IUSR here: link. You can set modify permissions on companydata* for the IUSR account and you can add this user to the IIS_IUSRS group and use that useraccount to run your application pool under. You only need to grand permissions for IIS_IUSRS on shared folders (TMP for instance), if you have multiple IUSR_accounts. – Pander

Jan, I always thought that IUSR was part of the IIS_IUSRS group by default? How can you check if this is so, as the IUSR account is a built-in account. Are you saying that I should uncheck Modify for IIS_USRS and check it for IUSR instead? Given the single-application requirement I don't think it will really make a difference will it? – Swerve

Answer 5

IIS_IUSRS group has prominence only if you are using ApplicationPool Identity. Even though you have this group looks empty at run time IIS adds to this group to run a worker process according to microsoft literature.

Unnecessarily

Not sure why this was downvoted. learn.microsoft.com/en-us/iis/get-started/planning-for-security/… – Bloem

Answer 6

I would use specific user (and NOT Application user). Then I will enable impersonation in the application. Once you do that whatever account is set as the specific user, those credentials would used to access local resources on that server (Not for external resources).

Specific User setting is specifically meant for accessing local resources.

Oralle