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 Directory Traversal vulnerability in gem installation that can result in the gem could write to arbitrary filesystem locations during installation. This attack appear to be exploitable via the victim must install a malicious gem. This vulnerability appears to have been fixed in 2.7.6.
blog.rubygems.org/2018/02/15/2.7.6-released.html
lists.opensuse.org/opensuse-security-announce/2019-07/msg00036.html
access.redhat.com/errata/RHSA-2018:3729
access.redhat.com/errata/RHSA-2018:3730
access.redhat.com/errata/RHSA-2018:3731
access.redhat.com/errata/RHSA-2019:2028
access.redhat.com/errata/RHSA-2020:0542
access.redhat.com/errata/RHSA-2020:0591
access.redhat.com/errata/RHSA-2020:0663
github.com/rubygems/rubygems/commit/666ef793cad42eed96f7aee1cdf77865db921099
github.com/rubygems/rubygems/commit/f83f911e19e27cbac1ccce7471d96642241dd759
lists.debian.org/debian-lts-announce/2018/07/msg00012.html
usn.ubuntu.com/3621-1/
www.debian.org/security/2018/dsa-4219
www.debian.org/security/2018/dsa-4259