网漏吞舟

wǎnglòu-tūnzhōu

[(of laws) too mild (to punish criminals)] 网里漏掉吞舟的大鱼, 比喻法令太宽, 使坏人漏网(见于《史记·酷吏列传序》: "网漏于吞舟之鱼")