Ruby before 2.4.2, 2.3.5, and 2.2.8 is vulnerable to a malicious format string which contains a precious specifier (*) with a huge minus value. Such situation can lead to a buffer overrun, resulting in a heap memory corruption or an information disclosure from the heap.
https://www.ruby-lang.org/en/news/2017/09/14/sprintf-buffer-underrun-cve-2017-0898/
https://www.debian.org/security/2017/dsa-4031
https://usn.ubuntu.com/3685-1/
https://security.gentoo.org/glsa/201710-18
https://lists.debian.org/debian-lts-announce/2018/07/msg00012.html
https://hackerone.com/reports/212241
https://github.com/mruby/mruby/issues/3722
https://access.redhat.com/errata/RHSA-2018:0585
https://access.redhat.com/errata/RHSA-2018:0583
https://access.redhat.com/errata/RHSA-2018:0378
https://access.redhat.com/errata/RHSA-2017:3485