This indicates an attack attempt to exploit a Denial of Service vulnerability in Apache Tomcat.
The vulnerability is due to an error when vulnerable software handles a crafted HTTP chunked Transfer coding. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system.
Apache Tomcat 8.0.0-RC1 to 8.0.3
Apache Tomcat 7.0.0 to 7.0.52
Apache Tomcat 6.0.0 to 6.0.39
Denial of Service: Remote attackers can crash vulnerable systems or services