Unlisted file extensions in URL requests must be filtered by any IIS 10.0 website.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-218758	IIST-SI-000230	SV-218758r695276_rule		Medium

Description
Request filtering enables administrators to create a more granular rule set to allow or reject inbound web content. Setting limits on web requests helps to ensure availability of web services and may also help mitigate the risk of buffer overflow type attacks. The allow unlisted property of the "File Extensions Request" filter enables rejection of requests containing specific file extensions not defined in the "File Extensions" filter. Tripping this filter will cause IIS to generate a Status Code 404.7.

Description

Request filtering enables administrators to create a more granular rule set to allow or reject inbound web content. Setting limits on web requests helps to ensure availability of web services and may also help mitigate the risk of buffer overflow type attacks. The allow unlisted property of the "File Extensions Request" filter enables rejection of requests containing specific file extensions not defined in the "File Extensions" filter. Tripping this filter will cause IIS to generate a Status Code 404.7.

STIG	Date
Microsoft IIS 10.0 Site Security Technical Implementation Guide	2021-12-28

Details

Check Text ( C-20231r695275_chk )
Follow the procedures below for each site hosted on the IIS 10.0 web server: Open the IIS 10.0 Manager. Click the site name. Double-click the "Request Filtering" icon. Click "Edit Feature Settings" in the "Actions" pane. If the "Allow unlisted file name extensions" check box is checked, this is a finding. Note: If this IIS 10.0 installation is supporting Microsoft Exchange, and not otherwise hosting any content, this requirement is Not Applicable. Note: If this IIS 10.0 installation is supporting Splunk, this requirement is Not Applicable.

Check Text ( C-20231r695275_chk )

Follow the procedures below for each site hosted on the IIS 10.0 web server:

Open the IIS 10.0 Manager.

Click the site name.

Double-click the "Request Filtering" icon.

Click "Edit Feature Settings" in the "Actions" pane.

If the "Allow unlisted file name extensions" check box is checked, this is a finding.

Note: If this IIS 10.0 installation is supporting Microsoft Exchange, and not otherwise hosting any content, this requirement is Not Applicable.

Note: If this IIS 10.0 installation is supporting Splunk, this requirement is Not Applicable.

Fix Text (F-20229r311173_fix)
Follow the procedures below for each site hosted on the IIS 10.0 web server: Open the IIS 10.0 Manager. Click the site name under review. Double-click the "Request Filtering" icon. Click "Edit Feature Settings" in the "Actions" pane. Uncheck the "Allow unlisted file extensions" check box.