どいつもこいつも conf/web.xml 見たことないのか？
標準でコメントアウトされてるのを復活させるだけだろが

<!-- Common Gateway Includes (CGI) processing servlet, which supports -->
<!-- execution of external applications that conform to the CGI spec -->
<!-- requirements. Typically, this servlet is mapped to the URL pattern -->
<!-- "/cgi-bin/*", which means that any CGI applications that are -->
<!-- executed must be present within the web application. This servlet -->
<!-- supports the following initialization parameters (default values -->
<!-- are in square brackets): -->

<servlet>
<servlet-name>cgi</servlet-name>
<servlet-class>org.apache.catalina.servlets.CGIServlet</servlet-class>