Can't access GeoServer after CORS filter

We had the same issue, after enabling CORS by removing the comments in web.xml original file supplied with GeoServer, GeoServer was no longer starting properly in any configuration (we tried using Mac OS X installer, with the platform independent binary and using Apache/Tomcat).

Finally, we managed to get the configuration to work using Apache/Tomcat but not using the default filter org.eclipse.jetty.servlets.CrossOriginFilter specified in web.xml supplied file but the Tomcat org.apache.catalina.filters.CorsFilter filter, as per https://enable-cors.org/server_tomcat.html (see also jgrocha answer at https://stackoverflow.com/questions/22363192/cors-tomcat-geoserver):

<filter>
  <filter-name>CorsFilter</filter-name>
  <filter-class>org.apache.catalina.filters.CorsFilter</filter-class>
</filter>
<filter-mapping>
  <filter-name>CorsFilter</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>

Have you check jar file in :

WEB-INF/lib/jetty-servlets*.jar

(not 'jetty-servlet'!)

If you don't have You can download in here.

and

You can check your Jetty version in :

[GEOSERVER_HOME]/lib