Unspecified file extensions on a production IIS 8.5 web server must be removed.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-76769	IISW-SV-000158	SV-91465r1_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
IIS 8.5 Server Security Technical Implementation Guide	2018-01-03

Details

Check Text ( C-76425r1_chk )
Open the IIS 8.5 Manager. Click the IIS 8.5 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-76425r1_chk )

Open the IIS 8.5 Manager.

Click the IIS 8.5 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-83465r1_fix)
Open the IIS 8.5 Manager. Click the IIS 8.5 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.