This indicates an attack attempt to exploit a Denial of Service attack in Apache Subversion.
The vulnerability is due to insufficient sanitizing of maliciously crafted requests. A remote attacker may be able to exploit this to cause denial of service conditions on the affected machine.
Apache Software Foundation Subversion prior to 1.8.16
Apache Software Foundation Subversion prior to 1.9.4
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the latest update from the vendor.