urlcheckformat in include/functions.inc.php in Piwigo before 2.8.3 allows remote attackers to bypass intended access restrictions via a URL that contains a " character, or a URL beginning with a substring other than the http:// or https:// substring.
Piwigo v2.8.2 has XSS via the tab, to, section, mode, installstatus, and display parameters of the admin.php file.