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Description

The following analytic leverages Event Id 4768, A Kerberos authentication ticket (TGT) was requested, to identify one source endpoint trying to obtain an unusual number Kerberos TGT ticket for non existing users. This behavior could represent an adversary abusing the Kerberos protocol to perform a user enumeration attack against an Active Directory environment. When Kerberos is sent a TGT request with no preauthentication for an invalid username, it responds with KRB5KDC_ERR_C_PRINCIPAL_UNKNOWN or 0x6. Red teams and adversaries alike may abuse the Kerberos protocol to validate a list of users use them to perform further attacks.\ The detection calculates the standard deviation for each host and leverages the 3-sigma statistical rule to identify an unusual number requests. To customize this analytic, users can try different combinations of the bucket span time and the calculation of the upperBound field.

  • Type: Anomaly

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

  • Last Updated: 2022-03-10
  • Author: Mauricio Velazco, Splunk
  • ID: d82d4af4-a0bd-11ec-9445-3e22fbd008af

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1589 Gather Victim Identity Information Reconnaissance
T1589.002 Email Addresses Reconnaissance
Kill Chain Phase
  • Reconnaissance
NIST
  • DE.AE
CIS20
  • CIS 10
CVE 


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 `wineventlog_security` EventCode=4768 Result_Code=0x6 Account_Name!="*$" 
| bucket span=2m _time 
| stats dc(Account_Name) AS unique_accounts values(Account_Name) as tried_accounts by _time, Client_Address 
| eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by Client_Address 
| eval upperBound=(comp_avg+comp_std*3) 
| eval isOutlier=if(unique_accounts > 10 and unique_accounts >= upperBound, 1, 0) 
| search isOutlier=1 
| `kerberos_user_enumeration_filter`

Macros

The SPL above uses the following Macros:

:information_source: kerberos_user_enumeration_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • EventCode
  • Result_Code
  • 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

Possible false positive scenarios include but are not limited to vulnerability scanners and missconfigured systems.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
24.0 30 80 Potential Kerberos based user enumeration attack $Client_Address$

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

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