Get Permission Microsoft issued patches Tuesday for four new critical vulnerabilities in the company's on-premises Exchange Server software. The flaws were discovered by the U.S. National Security Agency and disclosed to Microsoft. The company says customers using on-premises Exchange should prioritize these patches. "We have not seen the vulnerabilities used in attacks against our customers. However, given recent adversary focus on Exchange, we recommend customers install the updates as soon as possible to ensure they remain protected from these and other threats," the Microsoft Security Response Center says. The NSA joined with Microsoft in urging users to make the updates immediately.