Detection: Kerberos User Enumeration

Updated Date: 2024-05-25 ID: d82d4af4-a0bd-11ec-9445-3e22fbd008af Author: Mauricio Velazco, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects an unusual number of Kerberos Ticket Granting Ticket (TGT) requests for non-existing users from a single source endpoint. It leverages Event ID 4768 and identifies anomalies using the 3-sigma statistical rule. This behavior is significant as it may indicate an adversary performing a user enumeration attack against Active Directory. If confirmed malicious, the attacker could validate a list of usernames, potentially leading to further attacks such as brute force or credential stuffing, compromising the security of the environment.

Search

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

Data Source

Name	Platform	Sourcetype	Source	Supported App
Windows Event Log Security 4768	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Security'`	N/A

Macros Used

Name	Value
wineventlog_security	`eventtype=wineventlog_security OR Channel=security OR source=XmlWinEventLog:Security`
kerberos_user_enumeration_filter	`search *`

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

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1589	Gather Victim Identity Information	Reconnaissance
T1589.002	Email Addresses	Reconnaissance

KillChainPhase.RECONNAISSANCE

NistCategory.DE_AE

Cis18Value.CIS_10

APT32

FIN13

HEXANE

LAPSUS$

Magic Hound

APT32

EXOTIC LILY

HAFNIUM

HEXANE

Kimsuky

LAPSUS$

Lazarus Group

Magic Hound

Sandworm Team

Silent Librarian

TA551

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

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

Active Directory Kerberos Attacks

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
Potential Kerberos based user enumeration attack $src_ip$	24	30	80

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

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Security`	`XmlWinEventLog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Security`	`XmlWinEventLog`

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: GitHub | Version: 3