A specially crafted request could have crashed the Apache HTTP Server prior to version 2.4.30, due to an out of bound access after a size limit is reached by reading the HTTP header. This vulnerability is considered very hard if not impossible to trigger in non-debug mode (both log and build level), so it is classified as low risk for common server usage.
Exploitability
AV:NAC:HPR:NUI:NScope
S:UImpact
C:NI:NA:H5.9/CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H