RubyGems version Ruby 2.2 series: 2.2.9 and earlier, Ruby 2.3 series: 2.3.6 and earlier, Ruby 2.4 series: 2.4.3 and earlier, Ruby 2.5 series: 2.5.0 and earlier, prior to trunk revision 62422 contains a Improper Verification of Cryptographic Signature vulnerability in package.rb that can result in a mis-signed gem could be installed, as the tarball would contain multiple gem signatures.. This vulnerability appears to have been fixed in 2.7.6.
https://www.debian.org/security/2018/dsa-4259
https://www.debian.org/security/2018/dsa-4219
https://usn.ubuntu.com/3621-1/
https://lists.debian.org/debian-lts-announce/2019/05/msg00028.html
https://lists.debian.org/debian-lts-announce/2018/07/msg00012.html
https://lists.debian.org/debian-lts-announce/2018/04/msg00023.html
https://lists.debian.org/debian-lts-announce/2018/04/msg00001.html
https://lists.debian.org/debian-lts-announce/2018/04/msg00000.html
https://github.com/rubygems/rubygems/commit/f5042b879259b1f1ce95a0c5082622c646376693
https://access.redhat.com/errata/RHSA-2020:0663
https://access.redhat.com/errata/RHSA-2020:0591
https://access.redhat.com/errata/RHSA-2020:0542
https://access.redhat.com/errata/RHSA-2019:2028
https://access.redhat.com/errata/RHSA-2018:3731
https://access.redhat.com/errata/RHSA-2018:3730
https://access.redhat.com/errata/RHSA-2018:3729
http://lists.opensuse.org/opensuse-security-announce/2019-07/msg00036.html