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Description

The following analytic leverages Event 4768, A Kerberos authentication ticket (TGT) was requested, to identify a TGT request with encryption type 0x17, or RC4-HMAC. This encryption type is no longer utilized by newer systems and could represent evidence of an OverPass The Hash attack. Similar to Pass The Hash, OverPass The Hash is a form of credential theft that allows adversaries to move laterally or consume resources in a target network. Leveraging this attack, an adversary who has stolen the NTLM hash of a valid domain account is able to authenticate to the Kerberos Distribution Center(KDC) on behalf of the legitimate account and obtain a Kerberos TGT ticket. Depending on the privileges of the compromised account, this ticket may be used to obtain unauthorized access to systems and other network resources.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2022-03-04
  • Author: Mauricio Velazco, Splunk
  • ID: 18916468-9c04-11ec-bdc6-acde48001122

Annotations

ATT&CK
ID Technique Tactic
T1550 Use Alternate Authentication Material Defense Evasion, Lateral Movement
Kill Chain Phase
  • Exploitation
NIST
CIS20
CVE
1
2
 `wineventlog_security` EventCode=4768 Ticket_Encryption_Type=0x17 Account_Name!=*$ 
| `kerberos_tgt_request_using_rc4_encryption_filter` 

Macros

The SPL above uses the following Macros:

Note that kerberos_tgt_request_using_rc4_encryption_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required field

  • _time
  • EventCode
  • Ticket_Encryption_Type
  • Account_Name
  • Client_Address

How To Implement

To successfully implement this search, you need to be ingesting Domain Controller and Kerberos events. The Advanced Security Audit policy setting Audit Kerberos Authentication Service within Account Logon needs to be enabled.

Known False Positives

Based on Microsoft documentation, legacy systems or applications will use RC4-HMAC as the default encryption for TGT requests. Specifically, systems before Windows Server 2008 and Windows Vista. Newer systems will use AES128 or AES256.

Associated Analytic story

RBA

Risk Score Impact Confidence Message
25.0 50 50 A Kerberos TGT request with RC4 encryption was requested for $Account_Name$ from $Client_Address$

Reference

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

source | version: 1