Sssd: sssd: local denial of service due to null pointer dereference in pam responder

A flaw was found in SSSD (System Security Services Daemon). A local attacker with privileges to connect to the PAM (Pluggable Authentication Modules) responder socket can send a specially crafted protocol request. If the `pam_app_services` configuration is enabled and the service item is omitted from the request, a NULL pointer dereference can occur. This vulnerability leads to a denial of service, causing the PAM responder to crash and disrupt authentication services.