Ransomware-wielding attackers have begun to exploit a serious proxy-logon flaw in unpatched versions of Microsoft Exchange. Hackers have exploited the flaw to access vulnerable servers, crypto-lock files and demand a ransom. Microsoft on March 2 issued emergency patches to fix four zero-day flaws in Microsoft Exchange, which is one of the most widely used pieces of IT infrastructure in the world. The U.S. Cybersecurity and Infrastructure Security Agency also issued an emergency directive ordering agencies to investigate whether they had been compromised.”]
Source: https://www.healthcareinfosecurity.com/dearcry-ransomware-targets-unpatched-exchange-servers-a-16170