Krebsonsecurity quoted sourcesreport

Microsoft disclosed this week that hackers are exploiting four 0day vulnerabilities in exchange server v2013 to 2019. Within three days of the disclosure of the vulnerability, security experts said that the same hacker group increased attacks on the exchange server that has not been repaired, leaving a web shell that can be accessed later after the intrusion. Microsoft said it was working closely with the U.S. cybersecurity and infrastructure security agency to provide customers with the best guidance and mitigation measures.