By Juha Saarinen on Mar 16, 2021 12:27PM Halts first part of exploit chain. Microsoft has released a PowerShell script to help customers running its Exchange Server on-premises software to quickly and easily mitigate against an attack chain of vulnerabilities that is under heavy exploitation currently. The Exchange On-Premises Mitigation Tool or EOMT is recommended over Microsoft's earlier ExchangeMitigations.ps1 script, and handles the CVE-2021-26855 vulnerability through a uniform resource locator (URL) rewrite configuration. This, Microsoft said, mitigates against the known methods of exploiting the CVE-2021-26855 server-side request forgery authentication bypass vulnerability, which forms the first part of a four-stage attack chain that can lead to full system compromise.