Multiple Invalid Users Failing To Authenticate From Host Using Kerberos

Multiple Invalid Users Failing To Authenticate From Host Using Kerberos

Description

The following analytic identifies one source endpoint failing to authenticate with multiple invalid domain 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. As attackers progress in a breach, mistakes will be made. In certain scenarios, adversaries may execute a password spraying attack using an invalid list of users. Event 4768 is generated every time the Key Distribution Center issues a Kerberos Ticket Granting Ticket (TGT). Failure code 0x6 stands for client not found in Kerberos database (the attempted user is not a valid domain user).\ 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 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.

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Multiple Invalid Users Failing To Authenticate From Host Using Kerberos Help

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.

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