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.

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
Windows Event Log Security 4625 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Security'

Macros Used

Name Value
wineventlog_security eventtype=wineventlog_security OR Channel=security OR source=XmlWinEventLog:Security
windows_unusual_count_of_users_remotely_failed_to_auth_from_host_filter search *
windows_unusual_count_of_users_remotely_failed_to_auth_from_host_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
Agrius
Chimera
Ember Bear
HEXANE
Lazarus Group
Leafminer
Silent Librarian
APT28
APT38
APT39
APT41
Agrius
DarkVishnya
Dragonfly
Ember Bear
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 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

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
Potential password spraying attack on $Computer$ 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: 4