session_x11_req(Session *s)
{
	int success;

	if (s->auth_proto != NULL || s->auth_data != NULL) {
		error("session_x11_req: session %d: "
		    "x11 forwarding already active", s->self);
		return 0;
	}
	s->single_connection = packet_get_char();
	s->auth_proto = packet_get_string(NULL);
	s->auth_data = packet_get_string(NULL);
	s->screen = packet_get_int();
	packet_check_eom();

	if (xauth_valid_string(s->auth_proto) &&
	    xauth_valid_string(s->auth_data))
		success = session_setup_x11fwd(s);
	else {
		success = 0;
		error("Invalid X11 forwarding data");
	}
	if (!success) {
		free(s->auth_proto);
		free(s->auth_data);
		s->auth_proto = NULL;
		s->auth_data = NULL;
	}
	return success;
}

This category addresses vulnerabilities caused by flawed access control mechanisms, where incorrect permission settings allow unauthorized users to access restricted resources.