CISA and the NSA have jointly released “Microsoft Exchange Server Security Best Practices,” a guide to help organizations harden on-premises Exchange servers. This comes as threat activity targeting Exchange continues to persist, with unprotected servers remaining at high risk of compromise.
Business Impact
This new guidance signals that regulators and intelligence agencies view on-prem Exchange as a critical, ongoing national risk. Organizations that fail to implement these best practices may face increased scrutiny, higher breach likelihood, and potential non-compliance issues.
Why It Happened
Despite numerous zero-day exploits and subsequent patches over the years (like ProxyLogon, ProxyShell, and the recent CVE-2025-4421), attackers continuously find and exploit unpatched or misconfigured Exchange servers for data theft and ransomware deployment.
Recommended Executive Action
Direct your IT and security leaders to immediately review this new CISA/NSA guide. They should conduct a gap analysis against its recommendations and prioritize decommissioning any remaining end-of-life or hybrid Exchange servers to reduce the organizational attack surface.
Hashtags: #CISA #NSA #MicrosoftExchange #CyberSecurity #InfoSec #Hardening #BestPractices