The string_sanitize_url function in core/string_api.php in MantisBT 1.2.0a3 through 1.2.18 uses an incorrect regular expression, which allows remote attackers to conduct open redirect and phishing attacks via a URL with a ":/" (colon slash) separator in the return parameter to login_page.php, a different vulnerability than CVE-2014-6316.
https://www.mantisbt.org/bugs/view.php?id=17997
http://www.securitytracker.com/id/1031633