Microsoft Discloses Critical Exchange Server Vulnerability in Hybrid Setups

Microsoft disclosed a high-severity vulnerability in on-premise Exchange Server (CVE-2025-53786) that could allow attackers with admin access to escalate privileges in connected cloud environments, especially in hybrid setups. The flaw, which shares a service principal with Exchange Online, poses risks of undetectable privilege escalation and identity compromise if unpatched. Microsoft recommends applying the latest hotfix, reviewing security configurations, and resetting service principal keys if no longer used. CISA also warns about related malware exploiting recent SharePoint flaws and advises disconnecting outdated or end-of-life Exchange and SharePoint servers from the internet.