Windows Unusual Count Of Users Failed To Authenticate From Process

name: Windows Unusual Count Of Users Failed To Authenticate From Process
id: 25bdb6cb-2e49-4d34-a93c-d6c567c122fe
version: 12
creation_date: '2021-04-14'
modification_date: '2026-05-13'
author: Mauricio Velazco, Splunk
status: production
type: Anomaly
description: The following analytic identifies a source process failing to authenticate multiple users, potentially indicating a Password Spraying attack. It leverages Windows Event 4625, which logs failed logon attempts, and uses statistical analysis to detect anomalies. 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, the attacker could compromise multiple accounts, leading to unauthorized access, data exfiltration, or further lateral movement within the network.
data_source:
    - Windows Event Log Security 4625
search: |-
    `wineventlog_security`  EventCode=4625 Logon_Type=2 ProcessName!="-"
      | bucket span=2m _time
      | stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as user values(dest) as dest values(src) as src
        BY _time, ProcessName, SubjectUserName,
           Computer, action, app,
           authentication_method, signature, signature_id
      | eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std
        BY ProcessName, SubjectUserName, 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_failed_to_authenticate_from_process_filter`
how_to_implement: To successfully implement this search, you need to be ingesting Windows Event Logs from domain controllers aas 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 process failing to authenticate with multiple users is not a common behavior for legitimate user sessions. Possible false positive scenarios include but are not limited to vulnerability scanners and missconfigured systems.
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
intermediate_findings:
    entities:
        - field: user
          type: user
          score: 20
          message: Potential password spraying attack from $Computer$
        - field: Computer
          type: system
          score: 20
          message: Potential password spraying attack from $Computer$
analytic_story:
    - Active Directory Password Spraying
    - Insider Threat
    - Volt Typhoon
asset_type: Endpoint
mitre_attack_id:
    - T1110.003
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint