CISA is aware of widespread domestic and international exploitation of these vulnerabilities and strongly recommends organizations run the Test-ProxyLogon.ps1 script—as soon as possible—to help determine whether their systems are compromised. For additional information on the script, see Microsoft’s blog HAFNIUM targeting Exchange Servers with 0-day exploits.
For more information about these vulnerabilities and how to defend against their exploitation, see:
- Microsoft Advisory: Multiple Security Updates Released for Exchange Server
- Microsoft Blog: HAFNIUM targeting Exchange Servers with 0-day exploits
- Microsoft GitHub Repository: CSS-Exchange
- CISA Alert: Mitigate Microsoft Exchange Server Vulnerabilities
- CISA Emergency Directive 21-02: Mitigate Microsoft Exchange On-Premises Product Vulnerabilities