Name:Windows Unusual Count Of Users Fail To Auth Wth ExplicitCredentials id:14f414cf-3080-4b9b-aaf6-55a4ce947b93 version:4 date:2024-09-30 author:Mauricio Velazco, Splunk status:production type:Anomaly Description:The following analytic identifies a source user failing to authenticate with multiple users using explicit credentials on a host. It leverages Windows Event Code 4648 and calculates the standard deviation for each host, using the 3-sigma rule to detect anomalies. This behavior is significant as it may indicate a Password Spraying attack, where an adversary attempts to gain initial access or elevate privileges. If confirmed malicious, this activity could lead to unauthorized access, privilege escalation, or further compromise of the Active Directory environment. Data_source:
-Windows Event Log Security 4648
search:`wineventlog_security` EventCode=4648 Caller_User_Name!=*$ Target_User_Name!=*$ | bucket span=5m _time | stats dc(Target_User_Name) AS unique_accounts values(Target_User_Name) as user by _time, Computer, Caller_User_Name | eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by Computer | 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_fail_to_auth_wth_explicitcredentials_filter`
how_to_implement:To successfully implement this search, you need to be ingesting Windows Event Logs from domain controllers as well as member servers and workstations. The Advanced Security Audit policy setting `Audit Logon` within `Logon/Logoff` needs to be enabled. known_false_positives:A source user failing attempting to authenticate multiple users on a host is not a common behavior for regular systems. Some applications, however, may exhibit this behavior in which case sets of users hosts can be added to an allow list. Possible false positive scenarios include systems where several users connect to like Mail servers, identity providers, remote desktop services, Citrix, etc. References: -https://attack.mitre.org/techniques/T1110/003/ -https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4648 -https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/basic-audit-logon-events 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' - 'Insider Threat' - 'Volt Typhoon' asset_type:Endpoint confidence:70 impact:70 message:Potential password spraying attack from $Computer$ mitre_attack_id: - 'T1110.003' - 'T1110' observable: name:'user' type:'User' - role: - 'Victim' name:'Computer' - role: - 'Attacker' type:'Endpoint' product: - 'Splunk Enterprise' - 'Splunk Enterprise Security' - 'Splunk Cloud' required_fields: - '_time' - 'EventCode' - 'Target_User_Name' - 'Caller_User_Name' - 'Computer' risk_score:49 security_domain:endpoint
