In Ruby before 2.2.10, 2.3.x before 2.3.7, 2.4.x before 2.4.4, 2.5.x before 2.5.1, and 2.6.0-preview1, an attacker controlling the unpacking format (similar to format string vulnerabilities) can trigger a buffer under-read in the String#unpack method, resulting in a massive and controlled information disclosure.
http://lists.opensuse.org/opensuse-security-announce/2019-07/msg00036.html
https://access.redhat.com/errata/RHSA-2018:3729
https://access.redhat.com/errata/RHSA-2018:3730
https://access.redhat.com/errata/RHSA-2018:3731
https://access.redhat.com/errata/RHSA-2019:2028
https://lists.debian.org/debian-lts-announce/2018/04/msg00023.html
https://lists.debian.org/debian-lts-announce/2018/04/msg00024.html
https://lists.debian.org/debian-lts-announce/2018/07/msg00012.html
https://usn.ubuntu.com/3626-1/