Windows Multiple Invalid Users Failed To Authenticate Using NTLM

name: Windows Multiple Invalid Users Failed To Authenticate Using NTLM
id: 57ad5a64-9df7-11eb-a290-acde48001122
version: 13
creation_date: '2021-04-14'
modification_date: '2026-05-13'
author: Mauricio Velazco, Splunk
status: production
type: TTP
description: The following analytic detects a single source endpoint failing to authenticate with 30 unique invalid users using the NTLM protocol. It leverages EventCode 4776 from Domain Controller logs, focusing on error code 0xC0000064, which indicates non-existent usernames. 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, privilege escalation, and potential compromise of sensitive information within the Active Directory environment.
data_source:
    - Windows Event Log Security 4776
search: |-
    `wineventlog_security` EventCode=4776 TargetUserName!=*$ Status=0xc0000064
      | bucket span=5m _time
      | stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as tried_accounts values(dest) as dest
        BY _time, Workstation
      | where unique_accounts > 30
      | `windows_multiple_invalid_users_failed_to_authenticate_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 - "$Workstation$"
      search: '%original_detection_search% | search  Workstation = "$Workstation$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$Workstation$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$Workstation$") | 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"
finding:
    title: Potential NTLM based password spraying attack from $Workstation$
    entity:
        field: Workstation
        type: system
        score: 50
analytic_story:
    - Active Directory Password Spraying
    - Volt Typhoon
asset_type: Endpoint
mitre_attack_id:
    - T1110.003
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
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
      test_type: unit