Skype 3.6.0.248, and other versions before 3.8.0.139, uses a case-sensitive comparison when checking for dangerous extensions, which allows user-assisted remote attackers to bypass warning dialogs and possibly execute arbitrary code via a file: URI with a dangerous extension that uses a different case.
labs.idefense.com/intelligence/vulnerabilities/display.php?id=711
secunia.com/advisories/30547
www.securityfocus.com/bid/29553
www.securitytracker.com/id?1020201
www.skype.com/security/skype-sb-2008-003.html
www.vupen.com/english/advisories/2008/1749/references
exchange.xforce.ibmcloud.com/vulnerabilities/43044