The mail client in Opera before 8.50 opens attached files from the user's cache directory without warning the user, which might allow remote attackers to inject arbitrary web script and spoof attachment filenames.
https://exchange.xforce.ibmcloud.com/vulnerabilities/22335
http://www.vupen.com/english/advisories/2005/1789
http://www.securityfocus.com/bid/14880
http://www.securityfocus.com/advisories/9339
http://www.opera.com/docs/changelogs/windows/850/
http://www.opera.com/docs/changelogs/linux/850/
http://secunia.com/secunia_research/2005-42/advisory/