SQL agent jobs cause Audit failure in security log

Problem

When you audit your security log, something you are doing every day of course, you discover that SQL server is causing an audit failure fairly often:

image

Audit failure event 4625, The user account has expired:

image

Closer inspection reveals that the event is triggered by the SQL server engine service account. You could easily be lead to believe that the engine account itself has expired, as it is the only account mentioned by name in the error message. That is not the case here, as the “Account for which logon failed” is a null sid, also known as S-1-0-0 or nobody. This is Windows’ way of telling you that something failed, but I’m not going to say exactly what it was.

Analysis

The error appeared about every hour on the hour, so agent jobs is the top suspect. But the job logs disagreed, every job was working like a charm. Analysis of the central log repository revealed that the error appeared suddenly without any changes being made on the server at the time.

I discovered this on a cluster, so I tried failing over to another node. That didn’t change anything, the error followed sqlserver.exe to the other node. At least I had proven beyond reasonable doubt that the error was directly related to something SQL does. I was unable to find any fault on the server except from the audit failure. I checked all SQL server service accounts, none of which had an expiry date set. I drifted back to the agent jobs again, as agent job ownership has given me a hard time earlier. For some reason, if the person creating the jobs/maintenance plans is a sysadmin by group membership and not by direct membership, all agent jobs fail to execute unless you use a proxy account. I have blogged about this before though (http://lokna.no/?p=1267), so I always check for this when a new instance is installed and correct if necessary.

Then it struck me: there is a best practice somewhere stating that SQL Server installs are supposed to be executed as a special account, and not an account associated with the person that performs the installation. This is in case that person quits and we should delete his/her account. The agent jobs for backup, dbcc checkdb and such are usually created using another account though, but maybe there was an anomaly. I ran a quick check, and yes, the agent jobs were owned by the setup user. And this user was since marked as expired for security reasons, as it is only used  during setup and as a way into the server in case someone removes all other sysadmins and locks themselves out. I know there are other ways into a SQL Server you don’t have access to, but this is a lot easier as long as you have access to the domain.

To list job owners:

SELECT name, owner_sid FROM msdb.dbo.sysjobs

image

0x1 is sa, all the other jobs were owned by the setup user. These SIDs are in hex format. To convert to a username, run this:

SELECT SUSER_SNAME (0xHEXSID)

solution

Change the job and/or maintenance plan owner. See http://lokna.no/?p=325

Print This Post Print This Post

Tags:

Leave a Reply

%d bloggers like this: