Kerberos Authentication (AD)

The default authentication protocol in Active Directory, and the hub for every Kerberos attack in this wiki. Almost every technique here abuses one stage of this flow, one ticket, or one key — this page maps them all to where they hook in. For the ticket internals see tgt-tgs, kerberos-pac, kerberos-preauth, kerberos-encryption-types; for where tickets live see ccache and ticket-and-credential-opsec.

Core flow

AS-REQ / AS-REP — the client pre-authenticates (kerberos-preauth) to the KDC (on the DC) and receives a TGT, encrypted with the krbtgt key (krbtgt) and carrying the client’s PAC (kerberos-pac).
TGS-REQ / TGS-REP — the client presents the TGT to request a service ticket (TGS) for a target SPN (service-principal-name). The TGS is encrypted with the target service account’s key.
AP-REQ — the client presents the TGS to the service, which decrypts it with its own key. Delegation (kerberos-delegation) rides on top via S4U2self / S4U2proxy (s4u2self-s4u2proxy).

The full ticket model (TGT vs TGS, which key signs which, which attack hits which) is tgt-tgs.

The Kerberos attack map

Roasting (offline-crack a key exposed by the protocol)

Attack	What you crack	Page
Kerberoasting	a TGS encrypted with a service account key	kerberoasting
AS-REP Roasting	an AS-REP for a preauth-disabled user	as-rep-roasting
Targeted roasting	a victim you make roastable via an ACL write (SPN / UAC bit)	targeted-roasting
Timeroasting	a computer account password via MS-SNTP, unauthenticated	timeroasting

Ticket & PAC forgery (build a ticket from a secret or a flaw)

Attack	Secret / flaw	Page
Golden Ticket	forge a TGT with the `krbtgt` key	golden-silver-tickets
Silver Ticket	forge a TGS with a service key	golden-silver-tickets
Diamond Ticket	modify a real TGT’s PAC	diamond-ticket
Sapphire Ticket	inject a real privileged PAC via S4U2self	sapphire-ticket
Trust ticket	forge an inter-realm TGT with the trust key	trust-key-abuse
MS14-068	forge a PAC via broken signature validation (legacy)	ms14-068
noPac	sAMAccountName spoof → S4U2self ticket as a DC	nopac

Credential reuse (present a ticket/key you already hold)

Attack	Material	Page
Pass-the-Ticket	a stolen TGT/TGS	pass-the-hash-and-ticket
Overpass-the-Hash	an NT hash → a real KDC TGT	overpass-the-hash
Pass-the-Key	an AES key → a TGT	pass-the-key
Pass-the-Cert	a cert → PKINIT TGT	pass-the-cert

Delegation (impersonate via S4U)

Attack	Attribute	Page
Unconstrained	`TrustedForDelegation` → capture a TGT	unconstrained-delegation
Constrained	`msDS-AllowedToDelegateTo`	kerberos-delegation
RBCD	`msDS-AllowedToActOnBehalfOfOtherIdentity`	resource-based-constrained-delegation
S4U mechanics	S4U2self / S4U2proxy	s4u2self-s4u2proxy
Bronze Bit	flip the S4U2proxy forwardable bit (CVE-2020-17049)	bronze-bit

PKINIT / certificate path

Attack	Vector	Page
Shadow Credentials	write `msDS-KeyCredentialLink` → PKINIT	shadow-credentials
UnPAC-the-hash	recover the NT hash from a PKINIT PAC	pkinit-unpac-the-hash
AD CS (ESC1–16)	mint an auth cert → TGT	ad-cs-esc-attacks

Relay, persistence & gotchas

Kerberos relay — relay the AS/TGS exchange itself: krbrelay.
Skeleton Key — patch DC LSASS to accept a master key: skeleton-key.
The double-hop — why a WinRM/psexec second hop fails: kerberos-double-hop.
Ticket handling — kirbi/ccache, injection, purge: ccache, ticket-and-credential-opsec.

Detection (the shared signals)

4768 (AS-REQ/TGT) and 4769 (TGS-REQ) are the two core events — most Kerberos detection is correlating them: a 4769 with no 4768 (Silver / stolen ticket), a 4768 with no pre-auth (AS-REP roast, type 0), a 4768 from a non-DC host, an S4U 4769 where client ≠ service, or a machine account renamed to a DC (nopac). Full table: kerberos-event-ids.
RC4 (etype 0x17) downgrades in an AES domain — nearly every crack/forge benefits from RC4, so it’s a broad tell (kerberos-encryption-types).
Honey SPNs / honey accounts — cheap, high-fidelity (honeytokens).

Defenses (the shared mitigations)

gmsa — auto-rotated service secrets defeat Kerberoast/Silver cracking.
kerberos-armoring-fast (enforced) — kills AS-REP roasting and pre-auth brute; pairs with Protected Users (AES-only, no delegation, short TGT).
Disable RC4 (kerberos-encryption-types).
Rotate krbtgt twice after a suspected Golden/DCSync (krbtgt).
ad-tiering-and-hardening — the architectural blast-radius limit.