ID | Technique | Tactic |
---|---|---|
T1110.003 | Password Spraying | Credential Access |
T1110 | Brute Force | Credential Access |
Detection: Windows Unusual Count Of Users Failed To Authenticate Using NTLM
Description
The following analytic identifies a source endpoint failing to authenticate multiple valid users using the NTLM protocol, potentially indicating a Password Spraying attack. It leverages Event 4776 from Domain Controllers, calculating the standard deviation for each host and applying the 3-sigma rule to detect anomalies. This activity is significant as it may represent an adversary attempting to gain initial access or elevate privileges. If confirmed malicious, the attacker could compromise multiple accounts, leading to unauthorized access and potential lateral movement within the network.
Search
1`wineventlog_security` EventCode=4776 TargetUserName!=*$ Status=0xC000006A
2| bucket span=2m _time
3| stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as tried_accounts by _time, Workstation
4| eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by Workstation
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_using_ntlm_filter`
Data Source
Name | Platform | Sourcetype | Source | Supported App |
---|---|---|---|---|
Windows Event Log Security 4776 | 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_failed_to_authenticate_using_ntlm_filter | search * |
windows_unusual_count_of_users_failed_to_authenticate_using_ntlm_filter
is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Annotations
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 |
Implementation
To successfully implement this search, you need to be ingesting Domain Controller events. The Advanced Security Audit policy setting Audit Credential Validation
within Account Logon
needs to be enabled.
Known False Positives
A host failing to authenticate with multiple valid domain users is not a common behavior for legitimate systems. Possible false positive scenarios include but are not limited to vulnerability scanners and missconfigured systems. If this detection triggers on a host other than a Domain Controller, the behavior could represent a password spraying attack against the host's local accounts.
Associated Analytic Story
Risk Based Analytics (RBA)
Risk Message | Risk Score | Impact | Confidence |
---|---|---|---|
Potential NTLM based password spraying attack from $Workstation$ | 49 | 70 | 70 |
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