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.
https://www.tenable.com/security/tns-2019-09
https://www.debian.org/security/2018/dsa-4164
https://usn.ubuntu.com/3937-2/
https://usn.ubuntu.com/3627-2/
https://usn.ubuntu.com/3627-1/
https://support.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbux03909en_us
https://security.netapp.com/advisory/ntap-20180601-0004/
https://lists.debian.org/debian-lts-announce/2018/05/msg00020.html
https://httpd.apache.org/security/vulnerabilities_24.html
https://access.redhat.com/errata/RHSA-2019:0367
https://access.redhat.com/errata/RHSA-2019:0366
https://access.redhat.com/errata/RHSA-2018:3558
http://www.securitytracker.com/id/1040573