moodle before versions 3.5.2, 3.4.5, 3.3.8 is vulnerable to a boost theme - blog search GET parameter insufficiently filtered. The breadcrumb navigation provided by Boost theme when displaying search results of a blog were insufficiently filtered, which could result in reflected XSS if a user followed a malicious link containing JavaScript in the search parameter.
https://moodle.org/mod/forum/discuss.php?d=376025
https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2018-14631
http://www.securityfocus.com/bid/105371
http://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-62857