Name:Windows Unusual NTLM Authentication Users By Destination id:1120a204-8444-428b-8657-6ea4e1f3e840 version:2 date:2024-09-30 author:Steven Dick status:production type:Anomaly Description:The following analytic detects when a device is the target of numerous NTLM authentications using a null domain. This activity generally results when an attacker attempts to brute force, password spray, or otherwise authenticate to a domain joined Windows device from a non-domain device. This activity may also generate a large number of EventID 4776 events in tandem, however these events will not indicate the attacker or target device. Data_source:
-NTLM Operational 8004,8005,8006
search:`ntlm_audit` EventCode = 8004 SChannelName=* WorkstationName=* | eval src = replace(WorkstationName,"\\\\","") ```CIM alignment, remove leading \\ from some auth attempts ``` | eval dest = SChannelName, user = UserName ``` CIM alignment``` | where SChannelName!=src ``` Remove NTLM auths to self, improves accuracy for certain applications ``` | `windows_unusual_ntlm_authentication_users_by_destination_filter` | stats count min(_time) as firstTime max(_time) as lastTime dc(eval(upper(user))) as unique_count by dest | eventstats avg(unique_count) as unique_avg , stdev(unique_count) as unique_std | eval upperBound_unique=(1+unique_avg+unique_std*3) ``` adjust formula for sensitivity``` | eval isOutlier=CASE(unique_count > upperBound_unique, 1, true(), 0) | where isOutlier==1 | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`
how_to_implement:The following analytic detects when an unusual number of NTLM authentications is attempted against the same destination. This activity generally results when an attacker attempts to brute force, password spray, or otherwise authenticate to a domain joined Windows device using an NTLM based process/attack. This same activity may also generate a large number of EventID 4776 events as well. known_false_positives:Vulnerability scanners, print servers, and applications that deal with non-domain joined authentications. Recommend adjusting the upperBound_unique eval for tailoring the correlation to your environment, running with a 24hr search window will smooth out some statistical noise. References: -https://attack.mitre.org/techniques/T1110/003/ -https://techcommunity.microsoft.com/t5/ask-the-directory-services-team/ntlm-blocking-and-you-application-analysis-and-auditing/ba-p/397191 -https://techcommunity.microsoft.com/t5/microsoft-defender-for-identity/enriched-ntlm-authentication-data-using-windows-event-8004/m-p/871827 -https://www.varonis.com/blog/investigate-ntlm-brute-force -https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-nrpc/4d1235e3-2c96-4e9f-a147-3cb338a0d09f drilldown_searches: name:'View the detection results for - "$dest$"' search:'%original_detection_search% | search dest = "$dest$"' earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' name:'View risk events for the last 7 days for - "$dest$"' search:'| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") 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' asset_type:Endpoint confidence:100 impact:25 message:The device [$dest$] was the target of $count$ NTLM authentications using $unique_count$ unique user accounts. mitre_attack_id: - 'T1110' - 'T1110.003' observable: name:'dest' type:'Hostname' - role: - 'Victim' product: - 'Splunk Enterprise' - 'Splunk Enterprise Security' - 'Splunk Cloud' required_fields: - '_time' - 'EventCode' - 'DomainName' - 'Security' - 'WorkstationName' risk_score:25 security_domain:endpoint
