ruby-mail: SMTP injection

Takeshi Terada (Mitsui Bussan Secure Directions, Inc.) released a whitepaper entitled "SMTP Injection via recipient email addresses" ( http://www.mbsd.jp/Whitepaper/smtpi.pdf). This whitepaper has a section discussing how one such vulnerability affected the 'mail' ruby gem (see section 3.1).

Whitepaper has all the specific details, but basically the 'mail' ruby gem module is prone to the recipient attack as it does not validate nor sanitize given recipient addresses. Thus, the attacks described in chapter 2 of the whitepaper can be applied to the gem without any modification. The 'mail' ruby gem itself does not impose a length limit on email addresses, so an attacker can send a long spam message via a recipient address unless there is a limit on the application's side. This vulnerability affects only the applications that lack input validation.