Looks like Tomcat Jasper, which Jetty uses, is not compatible with a SecurityManager.
$ jar -tvf ~/.m2/repository/org/apache/tomcat/tomcat-jasper/8.5.5/tomcat-jasper-8.5.5.jar | grep Privileged
1772 Wed Aug 31 20:51:46 MST 2016 org/apache/jasper/runtime/JspFactoryImpl$PrivilegedGetPageContext.class
1091 Wed Aug 31 20:51:46 MST 2016 org/apache/jasper/runtime/JspFactoryImpl$PrivilegedReleasePageContext.class
$ jar -tvf ~/.m2/repository/org/mortbay/jasper/apache-jsp/8.5.5/apache-jsp-8.5.5.jar | grep Privileged
1772 Thu Oct 27 16:03:32 MST 2016 org/apache/jasper/runtime/JspFactoryImpl$PrivilegedGetPageContext.class
1091 Thu Oct 27 16:03:32 MST 2016 org/apache/jasper/runtime/JspFactoryImpl$PrivilegedReleasePageContext.class
772 Thu Oct 27 16:03:32 MST 2016 org/apache/tomcat/util/security/PrivilegedGetTccl.class
868 Thu Oct 27 16:03:32 MST 2016 org/apache/tomcat/util/security/PrivilegedSetTccl.class
The class it attempts to load (org.apache.jasper.runtime.JspRuntimeLibrary$PrivilegedIntrospectHelper) simply does not exist in the jar files.
Not sure if there's anything that Jetty can do to fix this.