Proof-of-concept exploit code has been released online over the weekend for an actively exploited high severity vulnerability impacting Microsoft Exchange servers.
The security bug tracked as CVE-2021-42321 impacts on-premises Exchange Server 2016 and Exchange Server 2019 and was patched by Microsoft during this month’s Patch Tuesday.
On Sunday, almost two weeks after the CVE-2021-42321 patch was issued, researcher Janggggg published a proof-of-concept exploit for the Exchange post-auth RCE bug.
“Our recommendation is to install these updates immediately to protect your environment,” the company said, urging Exchange admins to patch the bug exploited in the wild.
If you haven’t yet patched this security vulnerability in your on-premises servers, you can generate a quick inventory of all Exchange servers in your environment that need updating using the latest version of the Exchange Server Health Checker script.
In August, threat actors also began scanning for and breaching Exchange servers by exploiting ProxyShell vulnerabilities after security researchers reproduced a working exploit.