Nextcloud Server before 10.0.1 & ownCloud Server before 9.0.6 and 9.1.2 suffer from Reflected XSS in the Gallery application. The gallery app was not properly sanitizing exception messages from the Nextcloud/ownCloud server. Due to an endpoint where an attacker could influence the error message, this led to a reflected Cross-Site-Scripting vulnerability.
github.com/nextcloud/gallery/commit/f9ef505c1d60c9041e251682e0f6b3daad952d58
github.com/owncloud/gallery/commit/b3b3772fb9bec61ba10d357bef42b676fa474eee
github.com/owncloud/gallery/commit/dc4887f1afcc0cf304f4a0694075c9364298ad8a
hackerone.com/reports/165686
nextcloud.com/security/advisory/?id=nc-sa-2016-009
owncloud.org/security/advisory/?id=oc-sa-2016-019