Detection: Windows Unusual Count Of Users Failed To Authenticate From Process

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.

Search

1 `wineventlog_security`  EventCode=4625 Logon_Type=2 ProcessName!="-" 
2| bucket span=2m _time 
3| stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as user by _time, ProcessName, SubjectUserName, Computer 
4| eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by ProcessName, SubjectUserName, 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_failed_to_authenticate_from_process_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 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.

Associated Analytic Story

• Active Directory Password Spraying

• Insider Threat

• 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