splunk_escuAnomaly

Windows Unusual Count Of Users Remotely Failed To Auth From Host

The following analytic identifies a source host failing to authenticate against a remote host with multiple users, potentially indicating a Password Spraying attack. It leverages Windows Event 4625 (failed logon attempts) and Logon Type 3 (remote authentication) to detect this behavior. This activity is significant as it may represent an adversary attempting to gain initial access or elevate privileges within an Active Directory environment. If confirmed malicious, this could lead to unauthorized access, privilege escalation, and further compromise of the network.

MITRE ATT&CK

T1110.003

Detection Query

`wineventlog_security`  EventCode=4625 Logon_Type=3 IpAddress!="-"
  | bucket span=2m _time
  | stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as tried_accounts values(dest) as dest values(src) as src values(user) as user
    BY _time, IpAddress, Computer,
       action, app, authentication_method,
       signature, signature_id
  | eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std
    BY IpAddress, 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_remotely_failed_to_auth_from_host_filter`

Author

Mauricio Velazco, Splunk

Created

2026-03-10

Data Sources

Windows Event Log Security 4625

References

Tags

Active Directory Password SprayingVolt Typhoon

Raw Content

name: Windows Unusual Count Of Users Remotely Failed To Auth From Host
id: cf06a0ee-ffa9-4ed3-be77-0670ed9bab52
type: Anomaly
version: 10
status: production
date: '2026-03-10'
author: Mauricio Velazco, Splunk
data_source:
    - Windows Event Log Security 4625
description: The following analytic identifies a source host failing to authenticate against a remote host with multiple users, potentially indicating a Password Spraying attack. It leverages Windows Event 4625 (failed logon attempts) and Logon Type 3 (remote authentication) to detect this behavior. This activity is significant as it may represent an adversary attempting to gain initial access or elevate privileges within an Active Directory environment. If confirmed malicious, this could lead to unauthorized access, privilege escalation, and further compromise of the network.
how_to_implement: To successfully implement this search, you need to be ingesting Windows Event Logs from domain controllers as 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 host failing to authenticate with multiple valid users against a remote host is not a common behavior for legitimate systems. Possible false positive scenarios include but are not limited to vulnerability scanners, remote administration tools, missconfigyred systems, etc.
references:
    - https://attack.mitre.org/techniques/T1110/003/
    - https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4625
    - https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventID=4625
    - https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/basic-audit-logon-events
drilldown_searches:
    - name: View the detection results for - "$Computer$"
      search: '%original_detection_search% | search  Computer = "$Computer$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$Computer$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$Computer$") 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: $info_max_time$
search: |-
    `wineventlog_security`  EventCode=4625 Logon_Type=3 IpAddress!="-"
      | bucket span=2m _time
      | stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as tried_accounts values(dest) as dest values(src) as src values(user) as user
        BY _time, IpAddress, Computer,
           action, app, authentication_method,
           signature, signature_id
      | eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std
        BY IpAddress, 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_remotely_failed_to_auth_from_host_filter`
rba:
    message: Potential password spraying attack on $Computer$
    risk_objects:
        - field: Computer
          type: system
          score: 20
    threat_objects: []
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_remote_spray_xml/windows-security.log
          source: XmlWinEventLog:Security
          sourcetype: XmlWinEventLog
      name: True Positive Test