CVE-2026-46491: SimpleSAMLphp casserver FileSystemTicketStore path traversal allows out-of-ticket-directory read/unserialize and conditional deletion

simplesamlphp-module-casserver builds file paths for the file-based CAS ticket store by directly concatenating the configured ticket directory with an attacker-controlled ticket identifier. Public CAS validation/proxy endpoints pass attacker-controlled ticket / pgt query parameters into this store.

In deployments using FileSystemTicketStore, a remote attacker can use path traversal sequences such as ../target.serialized to make the CAS server read and unserialize files outside the ticket directory. In the CAS 1.0 validation flow, the same attacker-selected path is also passed to deleteTicket() immediately after getTicket() returns, which can delete the target file when it is readable by the PHP process, deletable under the PHP process filesystem permissions, and unserializes to a value compatible with the ?array return type.