CVE-2025-26647: 
vulnerability analysis and mitigation

A Windows Kerberos elevation-of-privilege vulnerability (CVE-2025-26647) was disclosed on April 8, 2025. This important-severity vulnerability affects Windows Server systems and stems from improper input validation in Windows Kerberos, allowing an unauthorized attacker to elevate privileges over a network. The vulnerability has a CVSS score of 8.1 (NVD, Microsoft Support).

The vulnerability requires network access but has high attack complexity, requiring specific conditions to be exploited. An authenticated attacker could exploit this vulnerability by establishing a machine-in-the-middle (MITM) attack or other local network spoofing technique, then sending a malicious Kerberos message to the client victim machine to spoof itself as the Kerberos authentication server. The vulnerability has been assigned CWE-20 (Improper Input Validation) and received a CVSS v3.1 base score of 8.1 (TechTarget).

If successfully exploited, this vulnerability allows attackers to gain elevated privileges through the Key Distribution Center. The vulnerability affects the Kerberos authentication protocol in Windows, potentially compromising the security of network authentication across affected Windows Server systems (Microsoft Support).

Microsoft has implemented a three-phase rollout for addressing this vulnerability. The initial deployment phase began with updates released on April 8, 2025, in audit mode. Even after installing the April Patch Tuesday update, Windows domain controllers require manual registry changes to enable protections. The second phase begins July 8, 2025, entering the Enforced by Default phase, allowing admins to switch back to Audit mode if needed. The final Enforcement phase starts October 14, 2025, removing the ability to make further registry changes (Microsoft Support).