This indicates an attack attempt against a Denial of Service vulnerability in Apache Tomcat.
The vulnerability is caused by an error when the vulnerable software handles crafted HTTP request packets. It allows a remote attacker to crash vulnerable systems.
Apache Software Foundation Tomcat prior to 6.0.43
Apache Software Foundation Tomcat prior to 7.0.55
Apache Software Foundation Tomcat prior to 8.0.8
Denial of Service: Remote attacker can crash vulnerable systems.
Apply the latest update from the vendor