城狐社鼠

chénghú-shèshǔ

[take advantage of one's or sb. else's power to do evils; the evildoes are like foxes in the city and rats in the temple] 要掏挖狐狸恐怕毁坏城池, 要熏死老鼠恐怕烧灼社庙。 比喻凭藉某种势力的庇护而作恶的人