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
Kill Chain Phase
1 2 `wineventlog_security` EventCode=4768 Ticket_Encryption_Type=0x17 Account_Name!=*$ | `kerberos_tgt_request_using_rc4_encryption_filter`
The SPL above uses the following Macros:
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.
List of fields required to use this analytic.
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
|25.0||50||50||A Kerberos TGT request with RC4 encryption was requested for $Account_Name$ from $Client_Address$|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
source | version: 1