I had posted here about how to extract account names with a specific modifier (exclude account names ending in a dollar sign.) That worked for one specific instance, but I found I needed something better. Active Directory logs have multiples of the same value (Account_Name, Group_Name, etc.) that all depend on context, namely the value of the line two lines above it.

For example,

Message=A member was added to a security-enabled universal group.

Subject:
 Security ID: <Random long SID>
 Account Name: Administrator
 Account Domain: ExampleDomain
 Logon ID: <random hex value>

Member:
 Security ID: <Another random long SID>
 Account Name: CN=George Clooney,OU=ExampleDomain,OU=Hollywood,OU=California,DC=USA,DC=NA,DC=Terra

Group:
 Security ID: <Yet another long SID>
 Account Name: Old Actors
 Account Domain: ExampleDomain

You can see that there are three different Security ID fields, three different Account Name fields, and two different Account Domain fields. The key is the context: Subject account name, member account name, or group account name.

I wrestled for some time to find a regex expression for Splunk that would continue matching things after a line has ended. After much searching I came across this post which explained the need for a regex modifier to do what I wanted.

In my case I needed to use the (?s) modifier to include newline characters in my extraction. My new and improved AD regex extraction is as follows:

(?s)(Group:.+Account Name:\s+)(?P<real_group_name>[^\n]+)

• (?s)  Regex modifier indicating to include new lines
• Group:  Section I am interested in. You can replace this with Member: if you’re interested in member account names instead
• .+ match one or more of any character (including new line as indicated by modifier above)
• Account Name:\s+ This is in conjuction with the previous two items to create a match that includes the section name and anything after that until the spaces after Account Name
• [^\n]+ Match one or more characters that is not a new line (since you might have an account name with spaces.)

Finally! This is the regex I’ve been looking for.

I don’t really understand Microsoft’s rationale when it comes to log verbosity. I suppose too much information is better than not enough information, but that comes at the cost of making it difficult if you have to try and actually read the information.

I’ve been trying to extract usernames from Active Directory controller logs and it turned out to be quite a pain. Why do the logs have more than one field with the same name? It confuses Splunk and seems to fly in the face of common sense and decency.. I will stop ranting now.

In my specific case, AD lockout logs have two Account Name fields, one for the controller and one for the user being locked out. I am interested only in the username and not the AD controller account name.  How do you tell Splunk to only include the second instance of Account Name?

The answer is to create a field extraction using negative lookahead (Thanks to this article which gave me the guidance I needed.) I had to tweak the regex to look for and exclude any matches ending in a dollar sign, as opposed to excluding dashes in the article’s example. My fine tuned regex statement is below:

Account Name:\s+(?!.+\$)(?P<FIELDNAME>\S+)

It looks for Account Name: followed by one or more spaces (there is excess spacing in the logs for some reason.) The real magic happens in the next bit – (?!.+\$)

• Parenthesis group the expression together
• ?! means negative lookahead – don’t include anything you find that matches the following regex
• .+ – one or more characters
• \$ – stop matching when you encounter a dollar sign

The second regex string is simply \S+ (one or more non-whitespace characters.)

Note this doesn’t satisfy all AD logs, just the ones I’m interested in (account lockouts – they all have a first Account Name ending in a dollar sign.)

The result of all this jargon and gnashing of teeth: clean Splunk logs revealing only what I want without excess information. Neat.

Update: I found an even better way to do this. The key is to use the regex modifier (?s) to include new lines. The better query is now this:

(?s)(<section name of the field you're interested in>:.+Account Name:\s+)(?P<real_group_name>[^\n]+)

A detailed explanation is located here.