Name:Kerberos User Enumeration id:d82d4af4-a0bd-11ec-9445-3e22fbd008af version:5 date:2024-09-30 author:Mauricio Velazco, Splunk status:production type:Anomaly 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. Data_source:
-Windows Event Log Security 4768
search:`wineventlog_security` EventCode=4768 Status=0x6 TargetUserName!="*$" | bucket span=2m _time | stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as tried_accounts by _time, src_ip | eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by src_ip | eval upperBound=(comp_avg+comp_std*3) | eval isOutlier=if(unique_accounts > 10 and unique_accounts >= upperBound, 1, 0) | search isOutlier=1| `kerberos_user_enumeration_filter`
how_to_implement:To successfully implement this search, you need to be ingesting Domain Controller and Kerberos events. The Advanced Security Audit policy setting `Audit Kerberos Authentication Service` within `Account Logon` needs to be enabled. known_false_positives:Possible false positive scenarios include but are not limited to vulnerability scanners and missconfigured systems. References: -https://github.com/ropnop/kerbrute -https://attack.mitre.org/techniques/T1589/002/ -https://redsiege.com/tools-techniques/2020/04/user-enumeration-part-3-windows/ drilldown_searches: name:'View the detection results for - "$src_ip$"' search:'%original_detection_search% | search src_ip = "$src_ip$"' earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' name:'View risk events for the last 7 days for - "$src_ip$"' search:'| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$src_ip$") starthoursago=168 | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`' earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' tags: analytic_story: - 'Active Directory Kerberos Attacks' asset_type:Endpoint confidence:80 impact:30 message:Potential Kerberos based user enumeration attack $src_ip$ mitre_attack_id: - 'T1589' - 'T1589.002' observable: name:'src_ip' type:'Endpoint' - role: - 'Victim' product: - 'Splunk Enterprise' - 'Splunk Enterprise Security' - 'Splunk Cloud' required_fields: - '_time' - 'EventCode' - 'Result_Code' - 'Account_Name' - 'Client_Address' risk_score:24 security_domain:endpoint
