Detection: Windows Unusual Count Of Users Fail To Auth Wth ExplicitCredentials

Description

The following analytic identifies a source user failing to authenticate with multiple users using explicit credentials on a host. It leverages Windows Event Code 4648 and calculates the standard deviation for each host, using the 3-sigma rule to detect anomalies. 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, or further compromise of the Active Directory environment.

Search

1`wineventlog_security` EventCode=4648 Caller_User_Name!=*$ Target_User_Name!=*$ 
2| bucket span=5m _time 
3| stats dc(Target_User_Name) AS unique_accounts values(Target_User_Name) as  user by _time, Computer, Caller_User_Name 
4| eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by 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_fail_to_auth_wth_explicitcredentials_filter`

Data Source

Name	Platform	Sourcetype	Source
Windows Event Log Security 4648	Windows	'xmlwineventlog'	'XmlWinEventLog:Security'

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 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.

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-4648

• 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: 4