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Hardening IIS

Revision as of 23:03, 16 August 2018 by Bill Sempf (talk | contribs) (Use an unique applicationPool per site)

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Draft - Work In Progress

Basic configuration

Common changes that should be part of all IIS installations.

Disable directoryBrowsing

Directory browsing gives the user the ability to just navigate to http://server/directory/ and get a list of all files in the directory. This was useful when web servers were primarily file servers, but is clearly a security problem now.

To disable directory browsing in IIS 10.0 (and several earlier versions, either:

1) Alter the web.config to set the directoryBrowse feature to false

        <directoryBrowse enabled="false" />

2) or Navigate to IIS in the Server Manager, and uncheck Directory Browsing under Common HTTP Features.

Avoid wildcard host headers

IIS 10.0 has added wildcard host headers. This means that if there is a website hosted for a domain, the server will handle requests for any subdomain, allowing the developer to make decisions based on the request as how to respond.

In general, this is a bad idea and shouldn't be used. There are very specific reasons to use them, but it is almost guaranteed that your situation isn't one of them.

Certainly, do not use wildcard domains, like http://* for example. But in general avoid using them at all. Instead use site bindings to solve the same problem.

Ensure applicationPoolIdentity is configured for all application pools

Use an unique applicationPool per site

Application bools are designed to create a collection of sites that can be restarted together, and have a common max memory limit, and some other features. With today's applications, it is best if there is a unique application pool for each site. Perhaps if there is a separate project for services and the front end of an application, then they could go together in one pool but for the majority of applications, one pool per app.=

There are two ways to configure application pools for IIS.

1)In IIS Manager, expand Sites in the Connections pane. Then click Advanced Settings, then the ellipsis button next to Application Pool. Select a unique pool there.

2) Using the command prompt, run appcmd to set up new command pools.

 appcmd.exe set config -section:system.applicationHost/applicationPools /+"[name='NewCommandPool',autoStart='True',managedPipelineMode='Integrated']" /commit:apphost

Disable IIS detailed error page from displaying remotely

Request filtering

Configure maxAllowedContentLength

Configure maxURL request filter

Configure MaxQueryString request filter

Reject non-ASCII characters in URLs

Reject double-encoded requests

Disable HTTP trace requests

Disallow unlisted file extensions

Enable Dynamic IP Address Restrictions

Transport Encryption

SSL/TLS settings are controlled at the SChannel level. They are set machine wide and IIS respects these values.

A list of recommendations for IIS

Disable SSL v2/v3

Disable TLS 1.0

Disable TLS 1.1

Ensure TLS 1.2 is enabled

Disable weak cipher suites (NULL cipher suites, DES cipher suites, RC4 cipher suites, Triple DES, etc)

Ensure TLS cipher suites are correctly ordered

HSTS support

IIS recently (Windows Server 1709) added turnkey support for HSTS

CORS support

If you choose not to handle CORS in your application, we ship an IIS an IIS module to help configure CORS


Sourabh Shirhatti (Microsoft)

Bill Sempf ([email protected])