Title

Unspecified file extensions on a production IIS 10.0 web server must be removed. (Cat II impact)

Discussion

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.

Check Content

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

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".

Additional Identifiers

Rule ID: SV-218824r961863_rule

Vulnerability ID: V-218824

Group Title: SRG-APP-000516-WSR-000174

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.