name: Windows Users Authenticate Using Explicit Credentials
id: e61918fa-9ca4-11eb-836c-acde48001122
version: 1
date: '2021-04-13'
author: Mauricio Velazco, Splunk
type: Anomaly
datamodel: []
description: 'The following analytic identifies a source user failing to authenticate
  with multiple users using explicit credentials on a host. This behavior could represent
  an adversary performing a Password Spraying attack against an Active Directory environment
  to obtain initial access or elevate privileges. Event 4648 is generated when a process
  attempts an account logon by explicitly specifying that accounts credentials. This
  event generates on domain controllers, member servers, and workstations.\

  The detection calculates the standard deviation for each host and leverages the
  3-sigma statistical rule to identify an unusual number of users. To customize this
  analytic, users can try different combinations of the `bucket` span time and the
  calculation of the `upperBound` field. This logic can be used for real time security
  monitoring as well as threat hunting exercises.\

  This detection will trigger on the potenfially malicious host, perhaps controlled
  via a trojan or operated by an insider threat, from where a password spraying attack
  is being executed.\

  The analytics returned fields allow analysts to investigate the event further by
  providing fields like source account, attempted user accounts and the endpoint were
  the behavior was identified.'
search: ' `wineventlog_security` EventCode=4648 | bucket span=2m _time | eval Source_Account
  = mvindex(Account_Name, 0) | eval Destination_Account = mvindex(Account_Name, 1)
  | search Source_Account != "*$" Source_Account !="-" Destination_Account !="*$"
  | stats dc(Destination_Account) AS unique_accounts values(Destination_Account) as
  tried_account by _time, ComputerName, Source_Account | eventstats avg(unique_accounts)
  as comp_avg , stdev(unique_accounts) as comp_std by ComputerName | eval upperBound=(comp_avg+comp_std*3)
  | eval isOutlier=if(unique_accounts > 10 and unique_accounts >= upperBound, 1, 0)
  | search isOutlier=1 | `windows_users_authenticate_using_explicit_credentials_filter` '
how_to_implement: To successfully implement this search, you need to be ingesting
  Windows Event Logs from domain controllers 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 source user failing attempting to authenticate multiple users
  on a host is not a common behavior for regular systems. Some applications, however,
  may exhibit this behavior in which case sets of users hosts can be added to an allow
  list. Possible false positive scenarios include systems where several users connect
  to like Mail servers, identity providers, remote desktop services, Citrix, etc.
references:
- https://attack.mitre.org/techniques/T1110/003/
- https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4648
- https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/basic-audit-logon-events
tags:
  analytic_story:
  - Active Directory Password Spraying
  - Insider Threat
  confidence: 70
  context:
  - Source:Endpoint
  - Stage:Initial Access
  - Stage:Privilege Escalation
  dataset:
  - https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1110.003/purplesharp_explicit_credential_spray/windows-security.log
  impact: 70
  kill_chain_phases:
  - Exploitation
  message: Potential password spraying attack from $ComputerName$
  mitre_attack_id:
  - T1110.003
  - T1110
  observable:
  - name: ComputerName
    type: Endpoint
    role:
    - Victim
  product:
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  required_fields:
  - _time
  - EventCode
  - Security_ID
  - Account_Name
  - ComputerName
  risk_score: 49
  security_domain: endpoint
  asset_type: Endpoint