Continuing my journey of learning the great AD FS Extranet Smart Lockout (ESL) feature.
As mentioned in my other post, the enhancement were made in AD FS 2016 auditing and there will be Event ID 1203 logged in the ADFS Security log by ADFS Auditing in case there was a failure to validate user credentials against Active Directory.
When you have enabled ADFS Extranet Smart Lockout feature in either log or enforce mode and AD FS Security auditing was enabled (the user has AD FS ESL bad password counts set to zero), as soon as the external bad password attempt count reaches the value specified in the ExtranetLockoutThreshold (you will see event ID 1203 for each bad password attempt), the account will be locked out on AD FS for a duration specified in the ExtranetObservationWindow, the event ID 1210 will be logged in Security event log and password validation attempts will not be sent to Active directory.
As mentioned in AD FS ESL public documentation:
AD FS will write extranet lockout events to the security audit log:
- When a user is locked out (reaches the lockout threshold for unsuccessful login attempts)
- When AD FS receives a login attempt for a user who is already in lockout state
At the same time, no event ID 1203 will be logged, since no password validation against Active Directory is taking place.
Only after the extranet observation window expires, the password attempts will be forwarded to AD and if the password validation fails, the event ID 1203 is logged.
Please note, that the CurrentBadPasswordCount value in event ID 1210 only increases when the password validation happens against AD and at the time the account is locked on AD FS.
Also keep in mind, that when the AD FS ESL extranet observation window expires, it doesn’t clear the AD FS ESL bad password count until good password was provided, so one single 1203 event from the same bad IP location with no bad password counts cleared will put account in ESL state again for the time specified in the ExtranetObservationWindow.
Hope this information will be helpful for you.