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 Software Foundation Tomcat 6.0.0 prior to 6.0.39
Apache Software Foundation Tomcat 7.0.0 prior to 7.0.50
Apache Software Foundation Tomcat 8.0.0-RC1 to 8.0.0-RC5
Denial of Service: Remote attackers can crash vulnerable systems or services
Apply the most recent upgrade or patch from the vendor.