Double encoded URL requests must be prohibited by any IIS 8.5 website.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-214468	IISW-SI-000229	SV-214468r508659_rule		Medium

Description
Request filtering enables administrators to create a more granular rule set with which to allow or reject inbound web content. By setting limits on web requests, it ensures availability of web services and mitigates the risk of buffer overflow type attacks. When the “Allow double escaping” option is disabled it prevents attacks that rely on double-encoded requests.

STIG	Date
Microsoft IIS 8.5 Site Security Technical Implementation Guide	2021-12-28

Details

Check Text ( C-15677r310608_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 the "Allow double escaping" check box is checked, this is a finding.

Fix Text (F-15675r310609_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 double escaping" check box.