ErrorReportValve showServerInfo must be set to false.

The Error Report Valve is a simple error handler for HTTP status codes that will generate and return HTML error pages. It can also be configured to return pre-defined static HTML pages for specific status codes and/or exception types. Disabling showServerInfo will only return the HTTP status code and remove all CSS from the default non-error related HTTP responses.

As an elevated user on the Tomcat server run the following command:

sudo grep -i ErrorReportValve $CATALINA_BASE/conf/server.xml file.

If the ErrorReportValve element is not defined and showServerInfo set to "false", this is a finding.

EXAMPLE: <Host ...> ... <Valve className="org.apache.catalina.valves.ErrorReportValve" showServerInfo="false"/> ... </Host>

As a privileged user on the Tomcat server:

Edit the $CATALINA_BASE/conf/server.xml file.

Create or modify an ErrorReportValve <Valve> element nested beneath each <Host> element.

EXAMPLE: <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="false"> ... <Valve className="org.apache.catalina.valves.ErrorReportValve" showServerInfo="false" /> ... </Host>

Restart the Tomcat server: sudo systemctl restart tomcat sudo systemctl daemon-reload