Cross-site scripting (XSS) vulnerability in the external_format_text function in lib/externallib.php in Moodle through 2.5.9, 2.6.x before 2.6.11, 2.7.x before 2.7.8, and 2.8.x before 2.8.6 allows remote authenticated users to inject arbitrary web script or HTML into an external application via a crafted string that is visible to web services.
https://moodle.org/mod/forum/discuss.php?d=313685
http://www.securitytracker.com/id/1032358
http://www.securityfocus.com/bid/74726
http://openwall.com/lists/oss-security/2015/05/18/1
http://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-49718