At the start of the year, Microsoft detected four concerning zero-day exploits that have since been widely leveraged to attack on-premises versions of Microsoft Exchange Server.
Thankfully, Exchange Online users are not affected by these specific vulnerabilities, but if your organization uses on-premises Exchange, any account tied to that server may be at risk and any connected networks should be analyzed for further indications of compromise (IOC). As our previous OTO article shared, these exploits have given threat actors access to email accounts and the ability to install additional malware for persistence. It is recommended that all Exchange Servers be patched immediately by installing the latest updates outlined below.
Exchange Server 2010 – be sure to install the update, KB5000978, that was released on March 2, 2021.
Exchange Server 2013, 2016, and 2019 – install the update, KB5000871, that was released on March 2, 2021. While this can stop further attacks, the updates will not evict a threat actor that has already compromised the system. So additionally, it is recommended to externally validate the patch and investigate if any compromise has occurred.
To determine the exploit status of an Exchange server, it is recommended to scan the logs using a PowerShell script from the Exchange Management shell, Test-ProxyLogon.ps1, which checks the Exchange server and saves the report. The GitHub Repository containing the script and instructions on how to use it can be found here: https://github.com/microsoft/CSS-Exchange/tree/main/Security.
If you have already been exploited, every second matters in ensuring your data is secured and that any existing unauthorized access is eradicated. Schneider Downs has a team of Digital Forensics and Incident Response (DFIR) experts available to help 24x7x365 at 1-800-993-8937.
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