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.

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 Supported App
Windows Event Log Security 4648 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Security' N/A

Macros Used

Name Value
wineventlog_security eventtype=wineventlog_security OR Channel=security OR source=XmlWinEventLog:Security
windows_unusual_count_of_users_fail_to_auth_wth_explicitcredentials_filter search *
windows_unusual_count_of_users_fail_to_auth_wth_explicitcredentials_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1110.003 Password Spraying Credential Access
T1110 Brute Force Credential Access
KillChainPhase.EXPLOITAITON
NistCategory.DE_AE
Cis18Value.CIS_10
APT28
APT29
APT33
Chimera
HEXANE
Lazarus Group
Leafminer
Silent Librarian
APT28
APT38
APT39
DarkVishnya
Dragonfly
FIN5
Fox Kitten
HEXANE
OilRig
Turla

Default Configuration

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

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Risk Event True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

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

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
Potential password spraying attack from $Computer$ 49 70 70
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation Passing N/A N/A N/A
Unit Passing Dataset XmlWinEventLog:Security XmlWinEventLog
Integration ✅ Passing Dataset XmlWinEventLog:Security XmlWinEventLog

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: 3