title: Valid Users Failing to Authenticate from Single Source Using NTLM
id: f88bab7f-b1f4-41bb-bdb1-4b8af35b0470
description: Detects failed logins with multiple valid domain accounts from a single source system using the NTLM protocol.
status: experimental
author: Mauricio Velazco
date: 2021/06/01
modified: 2021/07/07
references:
    - https://docs.splunk.com/Documentation/ESSOC/3.22.0/stories/UseCase#Active_directory_password_spraying
tags:
    - attack.t1110.003
    - attack.initial_access
    - attack.privilege_escalation
logsource:
    product: windows
    service: security
detection:
    selection1:
        EventID: 4776
        Status: '*0xC000006A' #Account logon with misspelled or bad password.
    filter:
        TargetUserName: '*$'
    timeframe: 24h
    condition:
        - selection1 and not filter | count(TargetUserName) by Workstation > 10
falsepositives:
    - Terminal servers
    - Jump servers
    - Other multiuser systems like Citrix server farms
    - Workstations with frequently changing users
level: medium
