Windows Unusual NTLM Authentication Users By Source

Name:Windows Unusual NTLM Authentication Users By Source
id:80fcc4d4-fd90-488e-b55a-4e7190ae6ce2
version:10
date:None
author:Steven Dick
status:production
type:Anomaly
Description:The following analytic detects when an unusual number of NTLM authentications is attempted by the same source. 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 in as well.
Data_source:

• -NTLM Operational 8004
• -NTLM Operational 8005
• -NTLM Operational 8006

search:`ntlm_audit`
EventCode = 8004
SChannelName=*
WorkstationName=*

```CIM alignment, remove leading \\ from some auth attempts```
| eval src = replace(WorkstationName,"\\\\","")
| eval dest = SChannelName, user = UserName

``` Remove NTLM auths to self, improves accuracy for certain applications```
| where SChannelName!=src

| stats count min(_time) as firstTime
max(_time) as lastTime
dc(eval(upper(user))) as unique_count by src
| eventstats avg(unique_count) as unique_avg
stdev(unique_count) as unique_std

``` adjust formula for sensitivity```
| eval upperBound_unique=(1+unique_avg+unique_std*3)

| eval isOutlier=CASE(unique_count > upperBound_unique, 1, true(), 0)
| where isOutlier==1
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
| `windows_unusual_ntlm_authentication_users_by_source_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: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 - "$src$"'
 search:'%original_detection_search% | search src = "$src$"'
 earliest_offset:'$info_min_time$'
 latest_offset:'$info_max_time$'
 name:'View risk events for the last 7 days for - "$src$"'
 search:'| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$src$") | 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:'7d'
 latest_offset:'0'
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

tags:

tests:
 name:'True Positive Test'
 attack_data:
  data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1110.003/ntlm_bruteforce/ntlm_bruteforce.log
  source: XmlWinEventLog:Microsoft-Windows-NTLM/Operational
  sourcetype: XmlWinEventLog
 test_type:'unit'
manual_test:None