More information about this security flaw is available in the following bug: https://bugzilla.redhat.com/show_bug.cgi?id=2379554 Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
The flexmark-java package neither BuildRequires nor Requires either apache-commons-lang or apache-commons-lang3. I am at a loss to understand why this bug was filed.