tiki-register.php in TikiWiki before 1.9.7 allows remote attackers to trigger "notification-spam" via certain vectors such as a comma-separated list of addresses in the email field, related to lack of "a minimal check on email."
http://www.vupen.com/english/advisories/2006/4709
http://tikiwiki.cvs.sourceforge.net/tikiwiki/tiki/tiki-register.php?r1=1.68&r2=1.69
http://tikiwiki.cvs.sourceforge.net/tikiwiki/tiki/changelog.txt?r1=1.157.2.50&r2=1.157.2.51