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Security hardening pointers for web.config
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web.config.markdown

Security hardening web.config

For a complete template see this Gist

Disable tracing
<system.web>
  <trace enabled="false" />
</system.web>
Prevent applications running if debug=true
<system.web>
  <deployment retail="true"/>
</system.web>
Disable debug
<system.web>
  <compilation debug="false" />
</system.web>
Rename the cookie to something more obscure ASP.NET_SessionId
<system.web>
  <sessionState cookieName="s" />
</system.web>
Disable ASP.NET version HTTP header
<system.web>
  <httpRuntime enableVersionHeader="false" />
</system.web>
Secure cookies on HTTPS deployments

See httpCookies Element MSDN documentation for more information.

<system.web>
  <httpCookies httpOnlyCookies="false" requireSSL="false" />
</system.web>
Remove unwanted http headers
<system.webServer>
  <httpProtocol>
      <customHeaders>
        <remove name="Server" />
        <remove name="X-Powered-By" />
        <remove name="X-AspNet-Version" />
        <remove name="X-AspNetMvc-Version" />
      </customHeaders>
    </httpProtocol>
</system.webServer>
Configure custome error handlers for specific HTTP error codes
<system.webServer>
  <httpErrors errorMode="Custom">
    <remove statusCode="502" subStatusCode="-1" />
    <remove statusCode="501" subStatusCode="-1" />
    <remove statusCode="500" subStatusCode="-1" />
    <remove statusCode="412" subStatusCode="-1" />
    <remove statusCode="406" subStatusCode="-1" />
    <remove statusCode="405" subStatusCode="-1" />
    <remove statusCode="404" subStatusCode="-1" />
    <remove statusCode="403" subStatusCode="-1" />
    <remove statusCode="401" subStatusCode="-1" />
    <remove statusCode="400" subStatusCode="-1" />
	
    <error statusCode="400" subStatusCode="-1" path="/error-handler.aspx" prefixLanguageFilePath="" responseMode="ExecuteURL" />
    <error statusCode="401" subStatusCode="-1" path="/error-handler.aspx" prefixLanguageFilePath="" responseMode="ExecuteURL" />
    <error statusCode="402" subStatusCode="-1" path="/error-handler.aspx" prefixLanguageFilePath="" responseMode="ExecuteURL" />
    <error statusCode="403" subStatusCode="-1" path="/error-handler.aspx" prefixLanguageFilePath="" responseMode="ExecuteURL" />
    <error statusCode="404" subStatusCode="-1" path="/error-handler.aspx" prefixLanguageFilePath="" responseMode="ExecuteURL" />
    <error statusCode="405" subStatusCode="-1" path="/error-handler.aspx" prefixLanguageFilePath="" responseMode="ExecuteURL" />
    <error statusCode="406" subStatusCode="-1" path="/error-handler.aspx" prefixLanguageFilePath="" responseMode="ExecuteURL" />
    <error statusCode="412" subStatusCode="-1" path="/error-handler.aspx" prefixLanguageFilePath="" responseMode="ExecuteURL" />
    <error statusCode="500" subStatusCode="-1" path="/error-handler.aspx" prefixLanguageFilePath="" responseMode="ExecuteURL" />
    <error statusCode="501" subStatusCode="-1" path="/error-handler.aspx" prefixLanguageFilePath="" responseMode="ExecuteURL" />
    <error statusCode="502" subStatusCode="-1" path="/error-handler.aspx" prefixLanguageFilePath="" responseMode="ExecuteURL" />
  </httpErrors>
</system.webServer>
Remove unwanted modules to reduce your attack surface
<system.webServer>
  <handlers>
    <remove name="TraceHandler-Integrated-4.0" />
    <remove name="TraceHandler-Integrated" />
    <remove name="AssemblyResourceLoader-Integrated-4.0" />
    <remove name="AssemblyResourceLoader-Integrated" />
    <remove name="WebAdminHandler-Integrated-4.0" />
    <remove name="WebAdminHandler-Integrated" />
    <remove name="HttpRemotingHandlerFactory-soap-ISAPI-2.0-64" />
    <remove name="svc-ISAPI-4.0_32bit" />
    <remove name="ScriptHandlerFactoryAppServices-Integrated-4.0" />
    <remove name="ScriptResourceIntegrated-4.0" />
    <remove name="svc-ISAPI-4.0_64bit" />
    <remove name="svc-Integrated-4.0" />
    <remove name="vbhtm-ISAPI-4.0_32bit" />
    <remove name="vbhtm-ISAPI-4.0_64bit" />
    <remove name="vbhtm-Integrated-4.0" />
    <remove name="vbhtml-ISAPI-4.0_32bit" />
    <remove name="vbhtml-ISAPI-4.0_64bit" />
    <remove name="vbhtml-Integrated-4.0" />
    <remove name="xamlx-ISAPI-4.0_32bit" />
    <remove name="xamlx-ISAPI-4.0_64bit" />
    <remove name="xamlx-Integrated-4.0" />
    <remove name="xoml-ISAPI-4.0_32bit" />
    <remove name="xoml-ISAPI-4.0_64bit" />
    <remove name="xoml-Integrated-4.0" />
    <remove name="HttpRemotingHandlerFactory-rem-Integrated-4.0" />
    <remove name="HttpRemotingHandlerFactory-rem-ISAPI-2.0" />
    <remove name="rules-ISAPI-4.0_32bit" />
    <remove name="rules-Integrated-4.0" />
    <remove name="HttpRemotingHandlerFactory-soap-Integrated" />
    <remove name="HttpRemotingHandlerFactory-soap-ISAPI-2.0" />
    <remove name="HttpRemotingHandlerFactory-soap-ISAPI-4.0_64bit" />
    <remove name="HttpRemotingHandlerFactory-soap-Integrated-4.0" />
    <remove name="HttpRemotingHandlerFactory-soap-ISAPI-4.0_32bit" />
    <remove name="rules-ISAPI-4.0_64bit" />
    <remove name="HttpRemotingHandlerFactory-rem-ISAPI-2.0-64" />
    <remove name="HttpRemotingHandlerFactory-rem-Integrated" />
    <remove name="HttpRemotingHandlerFactory-rem-ISAPI-4.0_32bit" />
    <remove name="HttpRemotingHandlerFactory-rem-ISAPI-4.0_64bit" />
    <remove name="AXD-ISAPI-2.0-64" />
    <remove name="cshtml-ISAPI-4.0_64bit" />
    <remove name="cshtml-Integrated-4.0" />
    <remove name="cshtm-Integrated-4.0" />
    <remove name="cshtml-ISAPI-4.0_32bit" />
    <remove name="cshtm-ISAPI-4.0_64bit" />
    <remove name="cshtm-ISAPI-4.0_32bit" />
    <remove name="AXD-ISAPI-4.0_64bit" />
    <remove name="AXD-ISAPI-2.0" />
    <remove name="AXD-ISAPI-4.0_32bit" />
    <remove name="PageHandlerFactory-ISAPI-2.0-64" />
    <remove name="PageHandlerFactory-ISAPI-2.0" />
    <remove name="PageHandlerFactory-ISAPI-4.0_64bit" />
    <remove name="PageHandlerFactory-ISAPI-4.0_32bit" />
    <remove name="aspq-ISAPI-4.0_64bit" />
    <remove name="aspq-Integrated-4.0" />
    <remove name="WebServiceHandlerFactory-ISAPI-2.0" />
    <remove name="aspq-ISAPI-4.0_32bit" />
    <remove name="WebServiceHandlerFactory-Integrated-4.0" />
    <remove name="WebServiceHandlerFactory-Integrated" />
    <remove name="SimpleHandlerFactory-ISAPI-4.0_64bit" />
    <remove name="SimpleHandlerFactory-Integrated-4.0" />
    <remove name="SimpleHandlerFactory-Integrated" />
    <remove name="SimpleHandlerFactory-ISAPI-2.0" />
    <remove name="SimpleHandlerFactory-ISAPI-2.0-64" />
    <remove name="WebServiceHandlerFactory-ISAPI-4.0_32bit" />
    <remove name="WebServiceHandlerFactory-ISAPI-4.0_64bit" />
    <remove name="WebServiceHandlerFactory-ISAPI-2.0-64" />
    <remove name="SimpleHandlerFactory-ISAPI-4.0_32bit" />
    <remove name="ISAPI-dll" />
    <remove name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" />
    <remove name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" />
    <remove name="OPTIONSVerbHandler" />
    <remove name="TRACEVerbHandler" />
  </handlers>
</system.webServer>
Restrict which HTTP verbs your application will work with
<system.webServer>
  <security>
    <requestFiltering allowHighBitCharacters="false">
      <verbs allowUnlisted="false">
        <add verb="GET" allowed="true" />
        <add verb="POST" allowed="true" />
      </verbs>
    </requestFiltering>
  </security>
</system.webServer>
Install iis-remove-server-headers module

Consider installing iis-remove-server-headers to remove common headers which leak undesirable information.

  • Server
  • X-Powered-By
  • X-AspNet-Version
  • X-AspNetMvc-Version
@eL-Prova

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eL-Prova commented Sep 1, 2017 •
edited

<httpCookies httpOnlyCookies="false" requireSSL="false" /> shouldn't be <httpCookies httpOnlyCookies="true" requireSSL="true" />

Further good practice:

<!-- Configure SSL URL Rewriting and IP filtering to block unwanted users -->
<system.webServer>
  <rewrite xdt:Transform="Insert">
    <rules>
      <rule name="HTTP to HTTPS redirect" stopProcessing="true">
        <match url="(.*)" />
        <conditions>
          <add input="{HTTPS}" pattern="off" ignoreCase="true" />
        </conditions>
        <action type="Redirect" redirectType="Found" url="https://{HTTP_HOST}/{R:1}" />
      </rule>
    </rules>
  </rewrite>
</system.webServer>
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