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.
http://www.securityfocus.com/bid/100862
http://www.securitytracker.com/id/1039363
https://access.redhat.com/errata/RHSA-2017:3485
https://access.redhat.com/errata/RHSA-2018:0378
https://access.redhat.com/errata/RHSA-2018:0583
https://access.redhat.com/errata/RHSA-2018:0585
https://github.com/mruby/mruby/issues/3722
https://hackerone.com/reports/212241
https://lists.debian.org/debian-lts-announce/2018/07/msg00012.html
https://security.gentoo.org/glsa/201710-18
https://usn.ubuntu.com/3685-1/
https://www.debian.org/security/2017/dsa-4031
https://www.ruby-lang.org/en/news/2017/09/14/sprintf-buffer-underrun-cve-2017-0898/
Source: MITRE
Published: 2017-09-15
Updated: 2018-07-15
Type: CWE-134
Base Score: 6.4
Vector: AV:N/AC:L/Au:N/C:P/I:N/A:P
Impact Score: 4.9
Exploitability Score: 10
Severity: MEDIUM
Base Score: 9.1
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Impact Score: 5.2
Exploitability Score: 3.9
Severity: CRITICAL