Microsoft has sent a fresh, urgent warning: Exchange Server is dealing with a high-severity vulnerability, CVE-2026-42897 (CVSS 8.1), and it’s already been classified as “exploited in the wild.” The impact is on on-prem Exchange deployments—Exchange Server 2016, Exchange Server 2019, and Exchange Subscription Edition (SE). Exchange Online is not affected. What makes this worse: the attack chain points to an OWA (Outlook Web Access) XSS issue. Attackers can craft messages to lure users into opening content in OWA. If specific user interactions happen, malicious scripts may run in the victim’s browser context—effectively giving the attacker a chance to act as the user, not just “drop malware and run.” No patch yet. Microsoft says the fix is still in development/testing and will land only after it meets quality standards—potentially first for some ESU participants. In the meantime, two mitigations are available: the Exchange Emergency Mitigation (EM) service (via IIS URL Rewrite + disabling vulnerable services/App Pools), and for offline/isolated setups, the Exchange on-premises Mitigation Tool (EOMT) executed through Exchange Management Shell. CISA has added this to KEV—federal orgs need mitigation by May 29. Time to stop the bleeding: assess exposure now, deploy mitigations, then patch. #CyberSecurity #MicrosoftExchange #OWA #CVE202642897 #KEV #ThreatIntel
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