Microsoft Defender Antivirus will now protect unpatched on-premises Exchange servers from ongoing attacks by automatically mitigating the actively exploited CVE-2021-26855 vulnerability. Microsoft has published ProxyLogon security updates for Microsoft Exchange Server 2019, 2016, and 2013, as well as step-by-step guidance to help address these ongoing attacks. Over 125,000 Exchange Servers still wait to be patched worldwide, according to Palo Alto Networks. Tens of thousands of organizations have already been compromised since January, two months before Microsoft started releasing patches.
Source: https://www.bleepingcomputer.com/news/security/microsoft-defender-adds-automatic-exchange-proxylogon-mitigation/