Windows Multiple NTLM Null Domain Authentications

name: Windows Multiple NTLM Null Domain Authentications
id: c187ce2c-c88e-4cec-8a1c-607ca0dedd78
version: 10
creation_date: '2024-03-16'
modification_date: '2026-05-13'
author: Steven Dick
status: production
type: TTP
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
    - NTLM Operational 8005
    - NTLM Operational 8006
search: '`ntlm_audit` EventCode IN (8004,8005,8006) DomainName=NULL UserName!=NULL | 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``` | stats count min(_time) as firstTime max(_time) as lastTime dc(eval(upper(user))) as unique_count dc(eval(upper(src))) as src_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)` | `windows_multiple_ntlm_null_domain_authentications_filter`'
how_to_implement: The following analytic requires that NTLM Operational logs to be imported from the environment Domain Controllers. This requires configuration of specific auditing settings, see Microsoft references for further guidance. This analytic is specific to EventID 8004~8006.
known_false_positives: 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
finding:
    title: The device [$dest$] was the target of $count$ NTLM authentications from $src_count$ sources using $unique_count$ unique user accounts.
    entity:
        field: dest
        type: system
        score: 50
analytic_story:
    - Active Directory Password Spraying
asset_type: Endpoint
mitre_attack_id:
    - T1110.003
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint