This indicates an attack attempt against a memory-corruption vulnerability in Apache Portable Runtime (APR) library.
The vulnerability is caused by an error when the vulnerable software handles a malicious WebDAV request. It allows a remote attacker to execute arbitrary code via sending a crafted web page.
Apache Portable Runtime (APR) library for Apache 2.0.37 through 2.0.45
Upgrade to version above Apache HTTP Server 2.0.46.