system sql consumes heavy CPU

Below SQL consumes heavy CPU

SELECT ATTR_NO, ATTR_NAME, ATTR_TYPE_NAME, ATTR_TYPE_OWNER FROM USER_TYPE_ATTRS WHERE TYPE_NAME IN (SELECT TABLE_NAME FROM ALL_SYNONYMS START WITH SYNONYM_NAME = : OWNER = 'PUBLIC' CONNECT BY NOCYCLE PRIOR TABLE_NAME = SYNONYM_NAME AND TABLE_OWNER = OWNER UNION SELECT : DUAL) ORDER BY ATTR_NO