system/libraries/Email.php in CodeIgniter before 3.1.3 allows remote attackers to execute arbitrary code by leveraging control over the email->from field to insert sendmail command-line arguments.
https://github.com/bcit-ci/CodeIgniter/pull/4966
https://github.com/bcit-ci/CodeIgniter/issues/4963
https://gist.github.com/Zenexer/40d02da5e07f151adeaeeaa11af9ab36