This indicates an attack attempt to exploit a Denial-Of-Service Vulnerability in Apache httpd.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted request. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system.
Apache Software Foundation httpd 2.4.6 to 2.4.29
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor: