Today my honeypot has been capturing scans for the Hazelcast REST API. I checked my logs for the past 2 years and these only started today. The last vulnerability published for Hazelcast was CVE-2018-10654 and related to “There is a Hazelcast Library Java Deserialization Vulnerability in Citrix XenMobile Server 10.8 before RP2 and 10.7 before RP3.”
There was some discussion regarding this issue at the end of Sep 2019 that got fixed at the end of Nov 2019  where /hazelcast/rest/cluster HTTP endpoint returns HTTP 500 status. If you are seeing similar discovery scans and when they started, we would like to hear from you.
(c) SANS Internet Storm Center. https://isc.sans.edu Creative Commons Attribution-Noncommercial 3.0 United States License.