The web application component of piSignage before 2.6.4 allows a remote attacker (authenticated as a low-privilege user) to download arbitrary files from the Raspberry Pi via api/settings/log?file=../ path traversal. In other words, this issue is in the player API for log download.
https://github.com/colloqi/piSignage/issues/97
https://github.com/colloqi/piSignage/blob/master/RELEASE%20NOTES.md
http://packetstormsecurity.com/files/155864/piSignage-2.6.4-Directory-Traversal.html