Description
Joomla! Core is prone to a spam vulnerability. Exploiting this issue may allow attackers to send spam through the affected website. Joomla! Core versions 1.5.x ranging from 1.5.0 and up to and including 1.5.22 are vulnerable.
Remediation
Update to Joomla! Core version 1.5.23 or latest
References
https://developer.joomla.org/joomlacode-archive/issue-24289.html
https://www.exploit-db.com/exploits/15979/
https://www.joomla.org/announcements/release-news/5367-joomla-1523-released.html