New Microsoft Exchange Server Vulnerability Allows Unauthorized Admin Privilege Escalation

Microsoft has disclosed a high-severity security vulnerability affecting Exchange Server hybrid deployments that could allow attackers with administrative access to escalate privileges and potentially compromise an organization’s entire cloud and on-premises infrastructure.

The vulnerability, tracked as CVE-2025-53786, was announced on August 6, 2025, prompting immediate action from cybersecurity agencies worldwide.

Vulnerability Overview

The Microsoft Exchange Server Hybrid Deployment Elevation of Privilege Vulnerability represents a significant security concern for organizations running hybrid Exchange environments.

This flaw allows cyber threat actors who have already obtained administrative access to an on-premises Microsoft Exchange server to escalate their privileges by exploiting vulnerable hybrid-joined configurations.

The vulnerability specifically targets the authentication mechanisms in hybrid deployments, potentially compromising the identity integrity of an organization’s Exchange Online service.

The vulnerability carries a CVSS score of 8.0 out of 10, categorized as “Important” severity by Microsoft.

The attack vector requires network access with high attack ...