Techniques
Sample rules
Kerberos User Enumeration
- source: splunk
- technicques:
- T1589
- T1589.002
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.
Detection logic
`wineventlog_security` EventCode=4768 Status=0x6 TargetUserName!="*$"
| bucket span=2m _time
| stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as tried_accounts by _time, src_ip
| eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by src_ip
| 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`