What happens after an attacker can issue Kerberos service tickets on behalf of a target user?

What Kerberos service-ticket forgery changes operationally

Once an attacker can mint service tickets for a target user, the problem is no longer just “a forged ticket exists”, it becomes “any service that trusts that ticket may now treat the attacker as the user”. In practical terms, the attacker can step through applications, file shares, and backend systems with the target’s effective rights, so the real blast radius depends on where that identity is trusted and what it can already reach.

That is why service-ticket abuse is often a domain movement problem rather than a single-host compromise. If the target user is highly privileged, the same forged-ticket capability can open administrative functions, management consoles, and remote service access without needing the original password or a local logon on the target endpoint. For background on how identity abuse becomes lateral movement and privilege escalation, see The 52 NHI breaches Report and the broader Ultimate Guide to NHIs section on identity types and trust relationships.

Kerberos makes this especially dangerous because the forged credential is designed to look like normal authentication material to the service, not like an obvious interactive login anomaly. That means the attacker’s next step is usually to enumerate what the impersonated user can access, then use those reachable services to deepen control, stage data theft, or move to higher-value systems. The attack is effective precisely because the trust decision is made by the receiving service, not by the compromised user’s workstation.

Why the impact depends on privilege, service scope, and ticket lifetime

The consequence is not identical for every target. A low-privilege user may still give access to useful data or an internal application, while a delegated admin, backup operator, or service owner account can expose far more sensitive functions. The ticket’s validity window also matters: the longer the service ticket remains accepted, the longer the attacker can reuse it for repeat access, pivoting, or quiet collection.

In mature environments, the services most at risk are often the ones with broad trust and weak segmentation, such as legacy business systems, file services, management endpoints, or apps that implicitly trust domain authentication. If the ticket can be used across multiple systems, one forged identity can become a stable foothold for lateral movement. For real-world patterns of credential abuse and downstream compromise, 52 NHI Breaches Analysis is a useful companion, and the generic attack mechanics are also reflected in CISA cyber threat advisories.

Because the attacker is operating through a valid-looking ticket, detection can lag behind impact. The activity may blend into routine Kerberos-authenticated traffic until someone correlates unusual service access, abnormal privilege use, or an access pattern that does not fit the target user’s normal behaviour. The security question is therefore not only “can the ticket be forged?” but “which services would actually honour it, and what can those services do on the attacker’s behalf?”

What defenders should verify when this attack path is possible

Once a forged-ticket path is on the table, defenders should treat service trust boundaries as the main control surface. The highest-value verification is whether sensitive services truly require the level of access they grant through Kerberos, whether administrative roles are tightly scoped, and whether ticket lifetime and service delegation settings are aligned with the minimum necessary access.

What to verify: Confirm which services accept Kerberos authentication for privileged functions, which accounts have broad access across multiple systems, and whether service-side logging can distinguish expected user activity from unusual lateral movement. Also verify that any forged-ticket scenario would still be constrained by segmentation, tiering, and least-privilege design rather than inherited domain trust alone.

Decision rule: If the forged ticket can reach a service that exposes administrative, data-export, or remote-execution capability, treat it as a privilege-escalation condition first and a detection problem second. If it only reaches a low-value service, the incident is still real, but the immediate priority shifts toward containment, access review, and service trust hardening.

Practitioner takeaway: The practical risk is not the forged Kerberos ticket by itself, it is the service access that the ticket unlocks, so the right response is to assess blast radius by trust scope rather than by the attacker’s initial foothold alone.

Related resources from NHI Mgmt Group

• What happens after an attacker hijacks a user session in Microsoft 365 or a similar workspace?
• What happens when a non-human identity token is exfiltrated and reused by an attacker?
• What happens when a newly created IAM user is immediately granted AdministratorAccess and added to a privileged group?
• What happens when a compromised service account is able to access cloud SaaS resources?