CVE-2024-29056Windows Kerberos PAC validation in cross-forest scenarios
What broke
CVE-2024-29056 is the cross-forest variant of CVE-2024-26248. PAC validation added after CVE-2022-37967 did not hold across a forest trust the way it held inside a forest. April 2024. Same staged-enforcement model.
Why it matters
Forest trusts are how M&A and resource forests still work. A PAC bypass across a trust is "we thought the resource forest was isolated." Identity architects who designed a red-forest or a resource forest around PAC integrity need this ID in the same change as 26248.
What to do
- Patch both sides of every trust. A patched account forest and an unpatched resource forest is not a mitigation.
- After enforcement, test TGS across the trust before you close the change.
- Review SID filtering and selective authentication. PAC bugs are how trust assumptions die.
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-2024-29056
- Microsoft PAC-validation servicing guidance, April 2024
Related identity CVEs
Related on Start with Identity
- CVEWindows Kerberos elevation of privilege
A 2026 Windows Kerberos elevation of privilege, patched by Microsoft. High severity. Read it next to KerberLoss and ResetNightmare: the 2026 AD year is a Kerber
- CVEWindows Kerberos information disclosure
A medium-severity Kerberos information-disclosure in Windows. Not a domain-compromise bug on its own, but it sits in the same 2025 Kerberos patch train as the S
- CVEWindows Kerberos PKINIT / NTAuth certificate logon bypass
The Windows KDC did not validate certificate-based logon (PKINIT) against NTAuth the way defenders thought. Remote elevation of privilege. Patched April 2025, w
- BlogKerberLoss: invisible Unicode lets an attacker twin a Kerberos SPN
CVE-2026-25177, CVSS 8.8. Active Directory treated look-alike SPNs as unique. Semperis and Shai Laron showed how that becomes service hijack and NTLM downgrade.
- BlogA CVE ID is a name. The value is knowing who the attacker becomes.
We opened a practitioner catalog of identity CVEs: what broke, why IAM teams should care, and what to do this week. Not an NVD mirror. A place to triage SAML wr
- BlogGoogle Workspace puts FIDO2 keys into the Windows login, days after Entra makes passkeys default
Google began rolling out FIDO2 security keys as a second factor at Windows sign-in for all Workspace customers on 13 July. Microsoft is making passkeys the defa