Unspecified file extensions on a production IIS 10.0 web server must be removed.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-218824	IIST-SV-000158	SV-218824r561041_rule		Medium

Description
By allowing unspecified file extensions to execute, the web servers attack surface is significantly increased. This increased risk can be reduced by only allowing specific ISAPI extensions or CGI extensions to run on the web server.

STIG	Date
Microsoft IIS 10.0 Server Security Technical Implementation Guide	2021-03-24

Details

Check Text ( C-20296r310947_chk )
Open the IIS 10.0 Manager. Click the IIS 10.0 web server name. Double-click the "ISAPI and CGI restrictions" icon. Click “Edit Feature Settings". Verify the "Allow unspecified CGI modules" and the "Allow unspecified ISAPI modules" check boxes are NOT checked. If either or both of the "Allow unspecified CGI modules" and the "Allow unspecified ISAPI modules" check boxes are checked, this is a finding.

Check Text ( C-20296r310947_chk )

Open the IIS 10.0 Manager.

Click the IIS 10.0 web server name.

Double-click the "ISAPI and CGI restrictions" icon.

Click “Edit Feature Settings".

Verify the "Allow unspecified CGI modules" and the "Allow unspecified ISAPI modules" check boxes are NOT checked.

If either or both of the "Allow unspecified CGI modules" and the "Allow unspecified ISAPI modules" check boxes are checked, this is a finding.

Fix Text (F-20294r310948_fix)
Open the IIS 10.0 Manager. Click the IIS 10.0 web server name. Double-click the "ISAPI and CGI restrictions" icon. Click "Edit Feature Settings". Remove the check from the "Allow unspecified CGI modules" and the "Allow unspecified ISAPI modules" check boxes. Click "OK".