Windows Unusual Count Of Invalid Users Failed To Auth Using NTLM

Name:Windows Unusual Count Of Invalid Users Failed To Auth Using NTLM
id:15603165-147d-4a6e-9778-bd0ff39e668f
version:10
date:2026-03-10
author:Mauricio Velazco, Splunk
status:production
type:Anomaly
Description:The following analytic identifies a source endpoint failing to authenticate with multiple invalid users using the NTLM protocol. It leverages EventCode 4776 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 or privilege escalation, posing a significant threat to the Active Directory environment. This detection is focused on domain controllers.
Data_source:

• -Windows Event Log Security 4776

search:`wineventlog_security` EventCode=4776 TargetUserName!=*$ Status=0xc0000064

| bucket span=2m _time

| stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as user values(dest) as dest
BY _time, Workstation

| eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std
BY Workstation

| eval upperBound=(comp_avg+comp_std*3)

| eval isOutlier=if(unique_accounts > 10 and unique_accounts >= upperBound, 1, 0)

| search isOutlier=1

| rename Workstation as src

| `windows_unusual_count_of_invalid_users_failed_to_auth_using_ntlm_filter`

how_to_implement:To successfully implement this search, you need to be ingesting Domain Controller events. The Advanced Security Audit policy setting `Audit Credential Validation' within `Account Logon` needs to be enabled.
known_false_positives:A host failing to authenticate with multiple invalid domain users is not a common behavior for legitimate systems. Possible false positive scenarios include but are not limited to vulnerability scanners and missconfigured systems. If this detection triggers on a host other than a Domain Controller, the behavior could represent a password spraying attack against the host's local accounts.
References:
  -https://attack.mitre.org/techniques/T1110/003/
  -https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/audit-credential-validation
  -https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4776
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'
    - 'Volt Typhoon'
  asset_type:Endpoint
  mitre_attack_id:
    - 'T1110.003'
  product:
    - 'Splunk Enterprise'
    - 'Splunk Enterprise Security'
    - 'Splunk Cloud'
  security_domain:endpoint

tests:
 attack_data:
  data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1110.003/purplesharp_invalid_users_ntlm_xml/windows-security.log
  source: XmlWinEventLog:Security
  sourcetype: XmlWinEventLog
 name:'True Positive Test'
manual_test:None