Name:Windows Unusual Count Of Users Failed To Auth Using Kerberos id:bc9cb715-08ba-40c3-9758-6e2b26e455cb version:3 date:2024-09-30 author:Mauricio Velazco, Splunk status:production type:Anomaly Description:The following analytic identifies a source endpoint failing to authenticate multiple valid users using the Kerberos protocol, potentially indicating a Password Spraying attack. It leverages Event 4771, which is generated when the Key Distribution Center fails to issue a Kerberos Ticket Granting Ticket (TGT) due to a wrong password (failure code 0x18). This detection uses statistical analysis, specifically the 3-sigma rule, to identify unusual authentication failures. If confirmed malicious, this activity could allow an attacker to gain initial access or elevate privileges within an Active Directory environment. Data_source:
-Windows Event Log Security 4771
search:`wineventlog_security` EventCode=4771 TargetUserName!="*$" Status=0x18 | bucket span=5m _time | stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as user by _time, IpAddress | eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by IpAddress | eval upperBound=(comp_avg+comp_std*3) | eval isOutlier=if(unique_accounts > 10 and unique_accounts >= upperBound, 1, 0) | search isOutlier=1 | `windows_unusual_count_of_users_failed_to_auth_using_kerberos_filter`
how_to_implement:To successfully implement this search, you need to be ingesting Domain Controller and Kerberos events. The Advanced Security Audit policy setting `Audit Kerberos Authentication Service` within `Account Logon` needs to be enabled. known_false_positives:A host failing to authenticate with multiple valid domain users is not a common behavior for legitimate systems. Possible false positive scenarios include but are not limited to vulnerability scanners, missconfigured systems and multi-user systems like Citrix farms. References: -https://attack.mitre.org/techniques/T1110/003/ -https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/dn319109(v=ws.11) -https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4771 drilldown_searches: name:'View the detection results for - "$user$"' search:'%original_detection_search% | search user = "$user$"' earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' name:'View risk events for the last 7 days for - "$user$"' search:'| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$") starthoursago=168 | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`' earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' tags: analytic_story: - 'Active Directory Password Spraying' - 'Active Directory Kerberos Attacks' - 'Volt Typhoon' asset_type:Endpoint confidence:70 impact:70 message:Potential Kerberos based password spraying attack from $IpAddress$ mitre_attack_id: - 'T1110.003' - 'T1110' observable: name:'user' type:'User' - role: - 'Victim' name:'IpAddress' - role: - 'Attacker' type:'Endpoint' product: - 'Splunk Enterprise' - 'Splunk Enterprise Security' - 'Splunk Cloud' required_fields: - '_time' - 'EventCode' - 'Status' - 'TargetUserName' - 'IpAddress' risk_score:49 security_domain:endpoint
