The vCard functions in Joomla! 1.0.5 use predictable sequential IDs for vcards and do not restrict access to them, which allows remote attackers to obtain valid e-mail addresses to conduct spam attacks by modifying the contact_id parameter to index2.php.
https://exchange.xforce.ibmcloud.com/vulnerabilities/24042
http://www.vupen.com/english/advisories/2006/0097
http://www.securityfocus.com/bid/16185
http://www.listerit.com/content/view/116/84/
http://secunia.com/advisories/18361