Unlisted file extensions in URL requests must be filtered by any IIS 8.5 website.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-76827	IISW-SI-000230	SV-91523r1_rule		Medium

Description
Request filtering enables administrators to create a more granular rule set to allow or reject inbound web content. By setting limits on web requests it 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. By setting limits on web requests it 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
IIS 8.5 Site Security Technical Implementation Guide	2018-04-06

Details

Check Text ( C-76483r1_chk )
Follow the procedures below for each site hosted on the IIS 8.5 web server: Open the IIS 8.5 Manager. Click on the site name. Double-click the "Request Filtering" icon. Click “Edit Feature Settings” in the "Actions" pane. If "Allow unlisted file extensions" check box is checked, this is a finding.

Fix Text (F-83523r1_fix)
Follow the procedures below for each site hosted on the IIS 8.5 web server: Open the IIS 8.5 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.