rubygems-update is an inbuilt rubygem for updating rubygems.
Affected versions of this package are vulnerable to DNS Hijack Attack. It does not validate the hostname when fetching gems or making API requests, which allows remote attackers to redirect requests to arbitrary domains via a crafted DNS SRV record with a domain that is suffixed with the original domain name, aka a DNS hijack attack. NOTE: this vulnerability exists because to an incomplete fix for
rubygems-update to version 2.0.17, 2.2.5, 2.4.8 or higher.