source: https://www.securityfocus.com/bid/12958/info

XM Forum is reported prone to a script injection vulnerability.

An attacker can supply arbitrary HTML and script code through the BBCode IMG tag to trigger this issue and execute arbitrary script code in a user's browser.

XM Forum RC3 is reported vulnerable. It is possible that other versions are affected as well. 

[IMG]javasc+ript:alert(document.cookie)[/IMG]