CVE-2026-62911 in Exchange Server
Summary
by MITRE • 08/11/2026
Authentication bypass by capture-replay in Microsoft Exchange Server allows an authorized attacker to elevate privileges over a network.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 08/12/2026
This vulnerability represents a critical authentication bypass flaw that exploits the capture-replay attack vector within Microsoft Exchange Server environments. The technical implementation involves an attacker leveraging previously captured authentication tokens or session data to gain unauthorized access to privileged network resources. This weakness stems from insufficient validation of authentication context and potentially flawed session management mechanisms that fail to properly verify the freshness and integrity of authentication credentials during subsequent access attempts.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass full network compromise potential. An authorized attacker who has previously captured valid authentication data can replay these credentials against Exchange Server services to obtain elevated privileges without requiring additional authentication factors or credentials. This creates a significant risk for organizations where Exchange Server serves as a central authentication hub or gateway to sensitive corporate resources.
The vulnerability demonstrates characteristics consistent with CWE-305 authentication flaw patterns, specifically involving improper handling of authentication tokens and session management failures. Attackers typically exploit this weakness by capturing valid authentication exchanges through network sniffing, packet analysis, or other passive monitoring techniques that allow them to collect session data or authentication tokens for later replay against the target system.
From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques under T1068 and credential access patterns in T1550. The attack chain typically begins with initial access through network reconnaissance or credential harvesting activities, followed by capture of valid session data that can be replayed against Exchange Server services to gain unauthorized elevated privileges.
Organizations should implement comprehensive mitigation strategies including enhanced session management protocols, token expiration mechanisms, and multi-factor authentication deployment across Exchange Server environments. Network segmentation and monitoring solutions should be deployed to detect anomalous authentication patterns and potential replay attack activities. Regular security updates and patch management processes must be prioritized to address known vulnerabilities in Exchange Server implementations.
Additional protective measures include implementing strict access controls, deploying robust intrusion detection systems, and establishing continuous monitoring for suspicious authentication behavior that may indicate token replay attacks. Security teams should also conduct regular vulnerability assessments targeting Exchange Server configurations to identify and remediate potential weaknesses in authentication handling mechanisms. The implementation of certificate-based authentication and time-based token validation can significantly reduce the attack surface associated with this particular vulnerability class.