The mailto (aka com_mailto) component in Joomla! 1.5 before 1.5.7 sends e-mail messages without validating the URL, which allows remote attackers to transmit spam.
developer.joomla.org/security/news/273-20080903-core-commailto-spam.html
marc.info/?l=oss-security&m=122115344915232&w=2
marc.info/?l=oss-security&m=122118210029084&w=2
marc.info/?l=oss-security&m=122152798516853&w=2
secunia.com/advisories/31789
securityreason.com/securityalert/4275
exchange.xforce.ibmcloud.com/vulnerabilities/45070