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

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-218824	SRG-APP-000516-WSR-000174	IIST-SV-000158	SV-218824r961863_rule	2025-02-11	3

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.

ℹ️ Check
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.

ℹ️ Check

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
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".