The MITRE CVE dictionary describes this issue as:
In Apache httpd 2.2.0 to 2.4.29, when generating an HTTP Digest authentication challenge, the nonce sent to prevent reply attacks was not correctly generated using a pseudo-random seed. In a cluster of servers using a common Digest authentication configuration, HTTP requests could be replayed across servers by an attacker without detection.
Find out more about CVE-2018-1312 from the
MITRE CVE dictionary dictionary and
The "AuthType Digest" directive is not enabled in the default httpd configuration as shipped with Red Hat Enterprise Linux, and needs to be explicitly enabled. Therefore this flaw has no impact on the default versions of the httpd package as shipped with Red Hat Enterprise Linux. Also upstream discourages the use of mod_auth_digest because of its inherent security weaknesses and recommends the use of mod_ssl.