The following analytic identifies one source endpoint failing to authenticate with 30 unique users using the Kerberos protocol. This behavior could represent an adversary performing a Password Spraying attack against an Active Directory environment using Kerberos to obtain initial access or elevate privileges. Active Directory environments can be very different depending on the organization. Users should test this detection and customize the arbitrary threshold when needed. Event 4771 is generated when the Key Distribution Center fails to issue a Kerberos Ticket Granting Ticket (TGT). Failure code 0x18 stands for
wrong password provided (the attempted user is a legitimate domain user).
This logic can be used for real time security monitoring as well as threat hunting exercises. This detection will only trigger on domain controllers, not on member servers or workstations.
The analytics returned fields allow analysts to investigate the event further by providing fields like source ip and attempted user accounts.
- Type: TTP
Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2021-04-08
- Author: Mauricio Velazco, Splunk
- ID: 3a91a212-98a9-11eb-b86a-acde48001122
Kill Chain Phase
- CIS 10
1 2 3 4 5 `wineventlog_security` EventCode=4771 TargetUserName!="*$" Status=0x18 | bucket span=5m _time | stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as tried_accounts by _time, IpAddress | where unique_accounts > 30 | `windows_multiple_users_failed_to_authenticate_using_kerberos_filter`
The SPL above uses the following Macros:
windows_multiple_users_failed_to_authenticate_using_kerberos_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 Domain Controller and Kerberos events. The Advanced Security Audit policy setting
Audit Kerberos Authentication Service 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, missconfigured systems and multi-user systems like Citrix farms.
Associated Analytic Story
|49.0||70||70||Potential Kerberos based password spraying attack from $IpAddress$|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
source | version: 2