Detection: Windows Unusual Count Of Users Remotely Failed To Auth From Host

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.

Search

1 `wineventlog_security`  EventCode=4625 Logon_Type=3 IpAddress!="-" 
2| bucket span=2m _time 
3| stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as tried_accounts by _time, IpAddress, Computer 
4| eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by IpAddress, Computer 
5| eval upperBound=(comp_avg+comp_std*3) 
6| eval isOutlier=if(unique_accounts > 10 and unique_accounts >= upperBound, 1, 0) 
7| search isOutlier=1 
8| `windows_unusual_count_of_users_remotely_failed_to_auth_from_host_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
Windows Event Log Security 4625	Windows	'xmlwineventlog'	'XmlWinEventLog:Security'	N/A

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

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.

Associated Analytic Story

• Active Directory Password Spraying

• Volt Typhoon

Risk Based Analytics (RBA)

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

Detection Testing

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 2