CVE-2025-26647Windows Kerberos PKINIT / NTAuth certificate logon bypass
What broke
The Windows Kerberos KDC accepted certificate-based logon (PKINIT) without the NTAuth store checks operators believed were in force. A crafted or mis-issued certificate becomes a domain logon. Microsoft patched this in April 2025 and tightened NTAuth enforcement. Getting the enforcement mode right is part of the fix, not an optional hardening note.
Why it matters
Certificate logon is how smart cards, Windows Hello for Business, and a lot of AD CS abuse become a TGT. Combined with CVE-2024-49019 (ESC15 / EKUwu) and the still-exploited Certifried mapping gap, 2025 was the year certificate authentication stopped being the "safe" Kerberos path.
What to do
- Deploy the April 2025 Kerberos updates on every DC.
- Audit the NTAuth store. Only your intended enterprise CAs belong there.
- Turn on strong certificate mapping (KB5014754) if it is not already in enforcement. CVE-2022-26923 is still showing up in incident response.
- Review AD CS templates for ESC1-ESC16, not only this CVE.
After you patch
Active Directory compromise is not contained by patching, because the artifacts an attacker creates outlive the vulnerability.
- Rotate the krbtgt account twice, with the replication interval between rotations, if there is any indication of ticket forgery. One rotation is not enough.
- Audit AD CS certificate templates for enrolment and enrollee-supplied-subject permissions, which are the most common escalation path left behind. See certificate lifecycle.
- Review privileged group membership and delegation rights (Domain Admins, DnsAdmins, constrained and resource-based constrained delegation) for changes during the window.
- Hunt for tickets with anomalous lifetimes or encryption types, and for authentications to services that identity never touches.
- Treat any issued certificate as a durable credential: revoking a user's password does not revoke a certificate that authenticates as them. See privilege escalation and lateral movement.
Sources
- NVD: CVE-2025-26647
- Microsoft April 2025 security updates, NTAuth enforcement guidance
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