The deliver function in the sendmail delivery agent (lib/mail/network/delivery_methods/sendmail.rb) in Ruby Mail gem 2.2.14 and earlier allows remote attackers to execute arbitrary commands via shell metacharacters in an e-mail address.
https://github.com/mikel/mail/raw/master/patches/20110126_sendmail.patch
https://exchange.xforce.ibmcloud.com/vulnerabilities/65010
http://www.vupen.com/english/advisories/2011/0233
http://www.securityfocus.com/bid/46021
http://secunia.com/advisories/43077
http://groups.google.com/group/mail-ruby/browse_thread/thread/e93bbd05706478dd?pli=1