Net::SMTP in Ruby before 2.4.0 is vulnerable to SMTP command injection via CRLF sequences in a RCPT TO or MAIL FROM command, as demonstrated by CRLF sequences immediately before and after a DATA substring.
https://www.debian.org/security/2017/dsa-3966
https://lists.debian.org/debian-lts-announce/2018/07/msg00012.html
https://hackerone.com/reports/137631
https://github.com/rubysec/ruby-advisory-db/issues/215
https://github.com/ruby/ruby/commit/0827a7e52ba3d957a634b063bf5a391239b9ffee