High Severity Vulnerability in Microsoft Exchange (CERT-EU Security Advisory 2025-030) On August 6, 2025, Microsoft issued an advisory for a high-severity vulnerability affecting Microsoft Exchange hybrid environments. The vulnerability tracked as CVE-2025-53786 allows an attacker with administrative access to an on-premises Exchange Server to escalate privileges into the connected Exchange Online environment. The vulnerability can impact the confidentiality, integrity, and availability of affected systems. https://www.cert.europa.eu/publications/security-advisories/2025-030/