From cysecurity.news
There have been updates published by Microsoft to address two severe zero-day vulnerabilities in Microsoft Exchange, collectively known as ProxyNotShell. These vulnerabilities have already been exploited and will continue to be exploited.
There is evidence that attackers have been chaining the two security flaws together to deploy Chinese Chopper web shells on compromised servers. As a result, they have been able to persist, steal data, as well as move laterally within the networks of their victims since September this year.