message/refresh.php in Moodle 1.9.x before 1.9.14 allows remote authenticated users to cause a denial of service (infinite request loop) via a URL that specifies a zero wait time for message refreshing.
https://bugzilla.redhat.com/show_bug.cgi?id=747444
http://moodle.org/mod/forum/discuss.php?d=188318
http://git.moodle.org/gw?p=moodle.git%3Ba=commit%3Bh=97f258fabb3ebfa7acc7c02cb59de92b01710f99