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Description

The following hunting analytic leverages Event ID 4769, A Kerberos service ticket was requested, to identify an unusual number of computer service ticket requests from one source. When a domain joined endpoint connects to a remote endpoint, it first will request a Kerberos Ticket with the computer name as the Service Name. An endpoint requesting a large number of computer service tickets for different endpoints could represent malicious behavior like lateral movement, malware staging, reconnaissance, etc.
The detection calculates the standard deviation for each host and leverages the 3-sigma statistical rule to identify an unusual number of service requests. To customize this analytic, users can try different combinations of the bucket span time, the calculation of the upperBound field as well as the Outlier calculation. This logic can be used for real time security monitoring as well as threat hunting exercises.\

  • Type: Hunting
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2021-12-01
  • Author: Mauricio Velazco, Splunk
  • ID: ac3b81c0-52f4-11ec-ac44-acde48001122

ATT&CK

ID Technique Tactic
T1078 Valid Accounts Defense Evasion, Persistence, Privilege Escalation, Initial Access
 `wineventlog_security` EventCode=4769 Service_Name="*$" Account_Name!="*$*" 
| bucket span=2m _time 
| stats dc(Service_Name) AS unique_targets values(Service_Name) as host_targets by _time, Client_Address, Account_Name 
| eventstats avg(unique_targets) as comp_avg , stdev(unique_targets) as comp_std by Client_Address, Account_Name 
| eval upperBound=(comp_avg+comp_std*3) 
| eval isOutlier=if(unique_targets >10 and unique_targets >= upperBound, 1, 0) 
| `unusual_number_of_computer_service_tickets_requested_filter`

Associated Analytic Story

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.

Required field

  • _time
  • EventCode
  • Ticket_Options
  • Ticket_Encryption_Type
  • dest
  • service
  • service_id

Kill Chain Phase

  • Reconnaissance
  • Exploitation
  • Lateral Movement

Known False Positives

An single endpoint requesting a large number of computer service tickets is not common behavior. Possible false positive scenarios include but are not limited to vulnerability scanners, administration systeams and missconfigured systems.

RBA

Risk Score Impact Confidence Message
42.0 70 60 None

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

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