Improper Neutralization of CRLF Sequences ('CRLF Injection')
The mail gem before 2.5.5 for Ruby (aka A Really Ruby Mail Library) 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.
CWE-93 - Improper Neutralization of CRLF Sequences ('CRLF Injection')
The software uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.