By specially crafting HTTP requests, the mod_md challenge handler would dereference a NULL pointer and cause the child process to segfault. This could be used to DoS the server. Fixed in Apache HTTP Server 2.4.34 (Affected 2.4.33)
id: CVE-2018-8011
info:
name: Apache HTTP Server - NULL Pointer Dereference
author: daffainfo
...