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Windows Event ID 4768 - A Kerberos authentication ticket was requested


Windows event ID 4768 is generated every time the Key Distribution Center (KDC) attempts to validate credentials.

Figure 1. Kerberos authentication protocol

Event ID 4768 (S) — Authentication Success

In cases where credentials are successfully validated, the domain controller (DC) logs this event ID with the Result Code equal to “0x0” and issues a Kerberos Ticket Granting Ticket (TGT) (Figure 1, Step 2).

Event ID 4768 (F) — Authentication Failure

If the provided credentials cannot be validated by the DC, event ID 4768 is logged instead with the Result Code not equal to “0x0”. (View all result codes.)

Access will not actually occur until a service ticket is granted, which is audited by event ID 4769.

Note: Event ID 4768 is logged for authentication attempts using the Kerberos authentication protocol. Refer to event ID 4776 for authentication attempts using NTLM authentication.

Figure 1. Event ID 4768 — General tab under Event Properties.

Event ID 4768 — General tab under Event Properties.

Figure 2. Event ID 4768 — Details tab under Event Properties.

Event ID 4768 — Details tab under Event Properties.

Description of the event fields.

Account Name: The name of the account for which a TGT was requested.

Note: Computer account name ends with a $.

User account example: mark
Computer account example: WIN12R2$

Supplied Realm Name: The name of the Kerberos Realm that the Account Name belongs to.

User ID: The SID of the account that requested a TGT. Event Viewer automatically tries to resolve SIDs and show the account name. If the SID cannot be resolved, you will see the source data in the event. For example, ADAPWS\mark or ADAPWS\WIN12R2$.

Service Name: The name of the service in the Kerberos Realm to which the TGT request was sent.

Service ID: The SID of the service account in the Kerberos Realm to which the TGT request was sent.

Client Address: The IP address of the computer from which the TGT request was received.

Client Port: The source port number of the client network connection. The Client Port is "0" for local (localhost) requests.

Ticket Options: A set of different ticket flags in hexadecimal format.

The most common values:
0x40810010 — Forwardable, Renewable, Canonicalize, Renewable-ok
0x40810000 — Forwardable, Renewable, Canonicalize
0x60810010 — Forwardable, Forwarded, Renewable, Canonicalize, Renewable-ok

Result Code: This is a set of different failure codes displayed in hexadecimal format. The result codes are listed in the following table:

Code Code name Description Possible causes
0x0 KDC_ERR_NONE No error No errors were found.
0x1 KDC_ERR_NAME_EXP Client's entry in KDC database has expired No information.
0x2 KDC_ERR_SERVICE_EXP Server's entry in KDC database has expired No information.
0x3 KDC_ERR_BAD_PVNO Requested Kerberos version number not supported No information.
0x4 KDC_ERR_C_OLD_MAST_KVNO Client's key encrypted in old master key No information.
0x5 KDC_ERR_S_OLD_MAST_KVNO Server's key encrypted in old master key No information.
0x6 KDC_ERR_C_PRINCIPAL_UNKNOWN Client not found in Kerberos database The username doesn’t exist.
0x7 KDC_ERR_S_PRINCIPAL_UNKNOWN Server not found in Kerberos database The DC can't find the server’s name in Active Directory.
0x8 KDC_ERR_PRINCIPAL_NOT_UNIQUE Multiple principal entries in KDC database Duplicate principal names exist.
Unique principal names are crucial for ensuring mutual authentication; duplicate principal names are strictly forbidden, even across multiple realms. Without unique principal names, the client has no way of ensuring that the server it's communicating with is the correct one.
0x9 KDC_ERR_NULL_KEY The client or server has a null key (master key) No master key was found for the client or server. This usually means that the administrator should reset the password on the account.
0xA KDC_ERR_CANNOT_POSTDATE Ticket (TGT) not eligible for postdating A client has requested postdating of a Kerberos ticket (setting the ticket’s start time to a future date/time), or there is a time difference between the client and the KDC.
0xB KDC_ERR_NEVER_VALID Requested start time is later than the end time There is a time difference between the KDC and the client.
0xC KDC_ERR_POLICY Requested start time is later than the end time There are logon restrictions on the user’s account, like a workstation restriction, smart card authentication requirement, or logon time restriction.
0xD KDC_ERR_BADOPTION KDC cannot accommodate requested option
  • The TGT is about to expire.
  • The client is attempting to delegate credentials to a SPN that's not in its Allowed-to-delegate-to list.
0xE KDC_ERR_ETYPE_NOTSUPP KDC has no support for encryption type The KDC or client received a packet that it can't decrypt.
0xF KDC_ERR_SUMTYPE_NOSUPP KDC has no support for checksum type The KDC, server, or client received a packet that it doesn’t have an appropriate encryption key for, so it can't decrypt the ticket.
0x10 KDC_ERR_PADATA_TYPE_NOSUPP KDC has no support for PADATA type (pre-authentication data)
  • Smart card logon is being attempted and the proper certificate can't be located. This can happen because the wrong certificate authority (CA) is being queried or the proper CA can't be contacted.
  • The DC doesn’t have a certificate installed for smart cards (Domain Controller or Domain Controller Authentication templates).

This error code can't occur in event 4768, but it can occur in 4771.

0x11 KDC_ERR_TRTYPE_NO_SUPP KDC has no support for transited type No information.
0x12 KDC_ERR_CLIENT_REVOKED Client’s credentials have been revoked There may be explicit restrictions on the account; the account could also be disabled, expired, or locked out.
0x13 KDC_ERR_SERVICE_REVOKED Credentials for server have been revoked No information.
0x14 KDC_ERR_TGT_REVOKED TGT has been revoked

Since the remote KDC may change its PKCROSS key while there are PKCROSS tickets still active, it should cache the old PKCROSS keys until the last issued PKCROSS ticket expires. Otherwise, the remote KDC will respond to a client with this error code.

See RFC1510 for more details.

0x15 KDC_ERR_CLIENT_NOTYET Client not yet valid—try again later No information.
0x16 KDC_ERR_SERVICE_NOTYET Server not yet valid—try again later No information.
0x17 KDC_ERR_KEY_EXPIRED Password has expired—change password to reset

The user’s password has expired.

This error code can't occur in event 4768, but it does occur in event 4771.

0x18 KDC_ERR_PREAUTH_FAILED Pre-authentication information was invalid

The wrong password was provided.

This error code can't occur in event 4768, but it does occur in event 4771.

0x19 KDC_ERR_PREAUTH_REQUIRED Additional pre-authentication required

Often occurs in UNIX interoperability scenarios. MIT-Kerberos clients do not request pre-authentication when they send a KRB_AS_REQ message. If pre-authentication is required (the default setting), Windows systems will send this error.

Most MIT-Kerberos clients will respond to this error by giving pre-authentication, in which case the error can be ignored.

0x1A KDC_ERR_SERVER_NOMATCH KDC does not know about the requested server No information.
0x1B KDC_ERR_SVC_UNAVAILABLE KDC is unavailable No information.
0x1F KRB_AP_ERR_BAD_INTEGRITY Integrity check on decrypted field failed The authenticator was encrypted with something other than the session key, so the client can't decrypt the resulting message. The modification of the message could be the result of an attack or network noise.
0x20 KRB_AP_ERR_TKT_EXPIRED The ticket has expired

The smaller the value for the Kerberos policy setting Maximum lifetime for user ticket, the more likely it is that this error will occur.

Because ticket renewal is automatic, you shouldn't have to do anything if you get this message.

0x21 KRB_AP_ERR_TKT_NYV The ticket is not yet valid

The clocks on the KDC and the client aren't synchronized.

If cross-realm Kerberos authentication is being attempted, then you should verify time synchronization between the KDC in the target realm and the KDC in the client realm.

0x22 KRB_AP_ERR_REPEAT The request is a replay A specific authenticator showed up twice; in other words, the KDC detected that this session ticket duplicates one that it has already received.
0x23 KRB_AP_ERR_NOT_US The ticket is not for us The server has received a ticket that was meant for a different realm.
0x24 KRB_AP_ERR_BADMATCH The ticket and authenticator do not match The KRB_TGS_REQ is being sent to the wrong KDC.
0x25 KRB_AP_ERR_SKEW The clock skew is too great A client computer sent a timestamp that exceeded the difference in value allowed by the Maximum tolerance for computer clock synchronization setting in Kerberos policy.
0x26 KRB_AP_ERR_BADADDR Network address in network layer header doesn't match address inside ticket
  • The address of the computer sending the ticket is different from the valid address in the ticket. A possible cause of this could be an IP address change
  • The ticket was passed through a proxy server or NAT. The client is unaware of the address scheme used by the proxy server, so unless the program caused the client to request a proxy server ticket with the proxy server's source address, the ticket could be invalid.
0x27 KRB_AP_ERR_BADVERSION Protocol version numbers don't match (PVNO) An application checks the KRB_SAFE message to verify that the protocol version and type fields match the current version and KRB_SAFE, respectively. A mismatch generates this error code.
0x28 KRB_AP_ERR_MSG_TYPE Message type is unsupported
  • The target server finds that the message format is wrong. This applies to KRB_AP_REQ, KRB_SAFE, KRB_PRIV, and KRB_CRED messages.
  • UDP protocol is being attempted with user-to-user authentication.
0x29 KRB_AP_ERR_MODIFIED Message stream modified and checksum didn't match
  • The authentication data was encrypted with the wrong key for the intended server.
  • The authentication data was modified in transit by a hardware or software error, or by an attacker.
  • Incorrect DNS data caused the client to send the request to the wrong server.
0x2A KRB_AP_ERR_BADORDER Message out of order (possible tampering)

This event is generated by KRB_SAFE and KRB_PRIV messages if an incorrect sequence number is included, or if a sequence number is expected but not present.

See RFC4120 for more details.

0x2C KRB_AP_ERR_BADKEYVER Specified version of key is not available This error might be generated on the server side when receiving an invalid KRB_AP_REQ message. The server can't use the key version indicated by the ticket in the KRB_AP_REQ (e.g. it indicates an old key that the server doesn't have copy of).
0x2D KRB_AP_ERR_NOKEY Service key not available

This error might be generated on the server side during receipt of an invalid KRB_AP_REQ message. The server doesn't have the right key to decipher the ticket.

Because it's possible for the server to be registered in multiple realms with different keys in each realm, the realm field in the unencrypted portion of the ticket in the KRB_AP_REQ is used to specify which secret key the server should use to decrypt that ticket.

0x2E KRB_AP_ERR_MUT_FAIL Mutual authentication failed No information.
0x2F KRB_AP_ERR_BADDIRECTION Incorrect message direction No information.
0x30 KRB_AP_ERR_METHOD Alternative authentication method required According to RFC4120, this error message is obsolete.
0x31 KRB_AP_ERR_BADSEQ Incorrect sequence number in message No information.
0x32 KRB_AP_ERR_INAPP_CKSUM Inappropriate type of checksum in message (checksum may be unsupported) When the KDC receives a KRB_TGS_REQ message, it decrypts it. Afterwards, the user-supplied checksum in the Authenticator must be verified against the contents of the request, and the message must be rejected if the checksums don't match (with an error code of KRB_AP_ERR_MODIFIED) or if the checksum isn't collision-proof (with an error code of KRB_AP_ERR_INAPP_CKSUM).
0x33 KRB_AP_PATH_NOT_ACCEPTED Desired path is unreachable No information.
0x34 KRB_ERR_RESPONSE_TOO_BIG Too much data

The size of a ticket is too large to be transmitted reliably via UDP.

In a Windows environment, this message is purely informational. A Windows computer will automatically try TCP if UDP fails.

0x3C KRB_ERR_GENERIC Generic error
  • Group membership has overloaded the Privilege Account Certificate (PAC).
  • Multiple recent password changes haven't been propagated.
  • Crypto subsystem error caused by running out of memory.
  • The SPN is too long
  • The SPN has too many parts.
0x3D KRB_ERR_FIELD_TOOLONG Field is too long for this implementation

If a KDC that doesn’t understand how to interpret a set high bit of the length encoding receives a request with the high order bit of the length set, it must return a KRB-ERROR message with the error KRB_ERR_FIELD_TOOLONG, and it must close the TCP stream.

Each request (KRB_KDC_REQ) and response (KRB_KDC_REP or KRB_ERROR) sent over the TCP stream is preceded by the length of the request as 4 octets in network byte order. The high bit of the length is reserved for future expansion and must currently be set to zero.

0x3E KDC_ERR_CLIENT_NOT_TRUSTED The client trust failed or is not implemented A user’s smart card certificate has been revoked, or the root CA that issued the smart card certificate (in a chain) is not trusted by the DC.
0x3F KDC_ERR_KDC_NOT_TRUSTED The KDC server trust failed or could not be verified

The trustedCertifiers field contains a list of CAs trusted by the client, just in case the client doesn't possess the KDC's public key certificate. If the KDC has no certificate signed by any of the trustedCertifiers, then it returns this error code.

See RFC1510 for more details.

0x40 KDC_ERR_INVALID_SIG The signature is invalid This error is related to PKINIT. If a PKI trust relationship exists, then the KDC verifies the client's signature on AuthPack (TGT request signature). If that fails, the KDC returns this error code.
0x41 KDC_ERR_KEY_TOO_WEAK A higher encryption level is needed f the clientPublicValue field is filled in, indicating that the client wishes to use Diffie-Hellman key agreement, then the KDC checks to see that the parameters satisfy its policy. If they do not (e.g. the prime size is insufficient for the expected encryption type), then the KDC returns this error code.
0x42 KRB_AP_ERR_USER_TO_USER_REQUIRED User-to-user authorization is required The client doesn't know that a service requires user-to-user authentication, so it requests, receives, and forwards a conventional KRB_AP_REP to the server; the server generates this error code in response.
0x43 KRB_AP_ERR_NO_TGT No TGT was presented or available A service doesn't have a TGT for user-to-user authentication.
0x44 KDC_ERR_WRONG_REALM Incorrect domain or principal

The client presents a cross-realm TGT to a realm other than the one specified in the TGT.

This error rarely occurs, but it’s typically caused by an incorrectly configured DNS.

Ticket Encryption Type: The cryptographic suite that was used while issuing the TGT.

Type Type Name Description
0x1 DES-CBC-CRC Disabled by default starting from Windows 7 and Windows Server 2008 R2.
0x3 DES-CBC-MD5 Disabled by default starting from Windows 7 and Windows Server 2008 R2.
0x11 AES128-CTS-HMAC-SHA1-96 Supported starting from Windows Server 2008 and Windows Vista.
0x12 AES256-CTS-HMAC-SHA1-96 Supported starting from Windows Server 2008 and Windows Vista.
0x17 RC4-HMAC Default suite for operating systems before Windows Server 2008 and Windows Vista.
0x18 RC4-HMAC-EXP Default suite for operating systems before Windows Server 2008 and Windows Vista.
0xFFFFFFFF or 0xffffffff - This type shows in Audit Failure events.

Pre-Authentication Type: The code number of the pre-authentication type which was used for the TGT request.

Error code Description Description
0 - Logon without pre-authentication.
2 PA-ENC-TIMESTAMPS Standard password authentication.

Additional pre-authentication required (accompanied by KRB-ERROR from the KDC). Usually used to notify a client of which key to use for encryption while sending a PA-ENC-TIMESTAMP pre-authentication value.

Never seen in Microsoft Active Directory environments.

15 PA-PK-AS-REP_OLD Used for smart card logon authentication.

Used for smart card authentication.

Never seen in certain Active Directory environments.


Additional pre-authentication required (accompanied by KRB-ERROR from the KDC). Usually used to notify a client of which key to use for encryption while sending a PA-ENC-TIMESTAMP pre-authentication value.

Never seen in Microsoft Active Directory environments.

20 PA-SVR-REFERRAL-INFO Used in KDC Referrals tickets.
138 PA-ENCRYPTED-CHALLENGE Logon using Kerberos Armoring (FAST). Supported in DCs running Windows Server 2012 and up, and clients running Windows 8 and up.
- - Shown in Audit Failure events.

Holds information regarding smart card certificates used during logon (if applicable).

Certificate Issuer Name: The name of the CA that issued the smart card certificate.

Certificate Serial Number: The smart card certificate’s serial number.

Certificate Thumbprint: The smart card certificate’s thumbprint.

Reasons to monitor event ID 4768

  • Monitor the Client Address field in event ID 4768 to track logon attempts that are outside your internal IP range.
  • Monitor for when the Result Code equals “0x6” (the username doesn't exist). If you see multiple events in a short span of time, this could be an indicator of account enumeration, reverse brute-force, or password spraying attacks, especially for highly-critical accounts.
  • Monitor event ID 4768 for accounts that have a Security ID that corresponds to high-value accounts, including administrators, built-in local administrators, domain administrators, and service accounts.
  • If a username is only to be used on an allowed list of IP addresses, you can monitor the Client Address field and trigger an alert whenever a logon attempt is made with a username that's not part of the white list.
  • If you have a list of accounts that are allowed to log on directly to DCs (rather than via network logon or Remote Desktop Connection), then monitor for when Client Address equals “::1” to identify violations and possible malicious intent.
  • Monitor Subject\Account Name for names that don’t comply with your company's naming conventions.
  • Monitor for accounts with a Security ID that corresponds to accounts that should never be used, including non-active, disabled, and guest accounts.
  • Monitor the 0x3F, 0x40, and 0x41 errors to more quickly identify smart card related problems with Kerberos authentication.
  • Monitor this event for account use outside of work hours to detect anomalies and potential malicious activity.

The need for an auditing solution:

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Although you can attach a task to the security log and ask Windows to send you an email, you are limited to simply getting an email whenever event ID 4768 is generated. Windows also lacks the ability to apply more granular filters that are required to meet security recommendations.

For example, Windows can send you an email every time event ID 4776 is generated, but it will not be able to only notify you on attempts from unauthorized endpoints, attempts occurring outside business hours, or attempts from expired, disabled, or locked accounts. Getting specific alerts reduces the chance of you missing out on critical notifications amongst a heap of false-positive alerts. Threshold-based alerts let you stay on top of any signs of malicious activity within your environment.

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The 8 Most
Critical Windows
Security Event IDs

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