The following analytic identifies a source user failing to authenticate with multiple users using explicit credentials on a host. This behavior could represent an adversary performing a Password Spraying attack against an Active Directory environment to obtain initial access or elevate privileges. Event 4648 is generated when a process attempts an account logon by explicitly specifying that accounts credentials. This event generates on domain controllers, member servers, and workstations.
The detection calculates the standard deviation for each host and leverages the 3-sigma statistical rule to identify an unusual number of users. To customize this analytic, users can try different combinations of the
bucket span time and the calculation of the
upperBound field. This logic can be used for real time security monitoring as well as threat hunting exercises.
This detection will trigger on the potenfially malicious host, perhaps controlled via a trojan or operated by an insider threat, from where a password spraying attack is being executed.
The analytics returned fields allow analysts to investigate the event further by providing fields like source account, attempted user accounts and the endpoint were the behavior was identified.
- Type: Anomaly
Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2022-09-22
- Author: Mauricio Velazco, Splunk
- ID: 14f414cf-3080-4b9b-aaf6-55a4ce947b93
Kill Chain Phase
- CIS 10
1 2 3 4 5 6 7 8 `wineventlog_security` EventCode=4648 Caller_User_Name!=*$ Target_User_Name!=*$ | bucket span=5m _time | stats dc(Target_User_Name) AS unique_accounts values(Target_User_Name) as tried_account by _time, Computer, Caller_User_Name | eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by Computer | eval upperBound=(comp_avg+comp_std*3) | eval isOutlier=if(unique_accounts > 10 and unique_accounts >= upperBound, 1, 0) | search isOutlier=1 | `windows_unusual_count_of_users_fail_to_auth_wth_explicitcredentials_filter`
The SPL above uses the following Macros:
windows_unusual_count_of_users_fail_to_auth_wth_explicitcredentials_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
List of fields required to use this analytic.
How To Implement
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
|49.0||70||70||Potential password spraying attack from $Computer$|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
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