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
- 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
Kill Chain Phase
1 2 3 4 5 6 7 8 `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`
The SPL above uses the following Macros:
Note that 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.
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
|24.0||30||80||Potential Kerberos based user enumeration attack $Client_Address$|
source | version: 1