CVE-2026-111053 FOSSBilling: Unauthenticated attacker can probe existence of arbitrary files via guest/system/template_exists

FOSSBilling is an open source billing and client-management platform. From 0.1.0 until 0.8.7, the unauthenticated api/guest/system/templateexists endpoint permits path traversal because templateExists uses Path::join on the attacker-controlled file parameter without rejecting .. sequences or...