What is a golden ticket attack, and why is it so dangerous?
An attacker who has obtained the KDC's own key (the krbtgt key) can forge TGTs for any user, with any group memberships and lifetime; the TGS accepts them because they decrypt with the right key, so the attacker effectively owns the realm.
The TGT is trusted for exactly one reason: it decrypts with the KDC key. If that key leaks, typically after an attacker gained domain-administrator rights and dumped the domain controller's database, they can mint TGTs offline:
- for any user, including non-existent ones or domain administrators,
- with any group memberships written into the ticket,
- with any lifetime, for example ten years.
No password is needed and no AS exchange takes place, which also makes the attack hard to spot. Changing the victims' passwords does not help, because the forgery depends only on the KDC key.
The remedy is to reset the krbtgt account's password twice (the KDC keeps the previous key for tickets in flight), waiting at least the maximum ticket lifetime in between, which invalidates all forged and genuine TGTs. This matches the disadvantage "if the Kerberos server is broken, all keys are compromised".
Go deeper:
MITRE ATT&CK: Golden Ticket (T1558.001) — the technique, real-world use and detection ideas.- Microsoft Learn: Reset the krbtgt password — the twice-with-a-pause procedure explained.