Catechism of the Catholic Church

Professional secrets-for example, those of political office holders, soldiers, physicians, and lawyers-or confidential information given under the seal of secrecy must be kept, save in exceptional cases where keeping the secret is bound to cause very grave harm to the one who confided it, to the one who received it or to a third party, and where the very grave harm can be avoided only by divulging the truth. Even if not confided under the seal of secrecy, private information prejudicial to another is not to be divulged without a grave and proportionate reason.