This indicates an attack attempt to exploit a Command Execution Vulnerability in Apache Subversion.
The vulnerability is due to an input validation error while parsing a crafted request. A remote attacker could exploit this to execute arbitrary code within the context of target application, via a crafted request.
Apache Software Foundation Subversion 1.0.0 through 1.8.18
Apache Software Foundation Subversion 1.9.0 through 1.9.6
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the latest update from the vendor.