Deploying a central auditing workspace with Log Analytics

Deploying a central auditing workspace with Log Analytics

One or multiple workspaces

A common question when talking Log Analytics design is one or multiple workspaces. Should there be one central workspace with all data? Should there be one workspace per application? Should there be one workspace for the auditing team? There are many different ideas and scenarios, but a common component is a central workspace for auditing. One workspace where a central team can track security-related events, assessments, and alerts.

The following topics are often involved when the decision to use one or multiple workspaces

  • In which region do we need to store the data, for example, the data must be stored within EU
  • Data Retention. The number of days to store the data is configured on a workspace level. That means that we will need to pay for the same retention setting on all our data within a workspace. If we have some data that needs to be stored for 7 days and some important data needs to be stored for 200 days, we will need to pay and store all data for 200 days.
  • Data Access. Today the workspace is the security boundary for Log Analytics. If we, for example, have log data from two different teams, that are not allowed to see each other’s data, we will need to store them in different workspaces.
  • Data Collection. Today there are solutions and data collection settings that are set on workspace level. For example, we enable collection of warnings in the Application log on Windows servers, it will be collected from all connected Windows servers, even if we only need it from some of our servers. This can affect the total cost in a negative way if collecting data not needed. In this scenario, it might be an idea to connect some servers to one workspace and others to another workspace.

When decided to use multiple workspaces it is possible to multi-home Windows servers to send data to multiple workspaces. For Linux servers and some other data sources, for example, multiple PaaS services can today send data to one workspace. One thing to note when configuring multi-home data sources is that if the same data is collected and inserted into multiple workspaces, we also pay for that data twice. In other words, it is a good idea to make sure that different kind of data is collected for each workspace, for example, audit data to one workspace and application logs to another.

The following figure describes a scenario where two application teams have their own workspaces, and there is one workspace for central auditing. The auditing team needs access to data from both service workspaces, to run analyzes and verify that everything is running according to company policies.

To deploy this scenario simple deploy three workspaces and give the central auditing team read permissions on each service workspace, see Microsoft Docs for more details.

Cross workspace queries

The next step is to start author queries to analyze and visualize the data. The data is stored in each service workspace so the Auditing team will need to use the cross-workspace query feature, read more about it (https://docs.microsoft.com/en-us/azure/log-analytics/log-analytics-cross-workspace-search). Data is only stored in the two service workspaces, there is no data in the central auditing workspace.

The following query is a cross workspace query example, query two workspaces and list failed logon events. In the query we use “isfuzzy” to tell Log Analytics that execution of the query will continue even if the underlying table or view reference is not present. We can also see the two workspace ID, one for each service workspace, and that we use the SecurityEvent table.

union isfuzzy=true
workspace(“b111d916-5556-4b3c-87cf-f8d93dad7ea0”).SecurityEvent, workspace(“0a9de77d-650f-4bb1-b12f-9bcdb6fb3652”).SecurityEvent
| where EventID == 4625 and AccountType == ‘User’
| extend LowerAccount=tolower(Account)
| summarize Failed = count() by LowerAccount
| order by Failed desc

The following example shows all failed security baseline checks for the two service workspaces

union isfuzzy=true
workspace(“b111d916-5556-4b3c-87cf-f8d93dad7ea0”).SecurityBaseline, workspace(“0a9de77d-650f-4bb1-b12f-9bcdb6fb3652”).SecurityBaseline
| where ( RuleSeverity == “Critical” )
| where ( AnalyzeResult == “Failed” )
| project Computer, Description

To make cross workspace queries a bit easier we can create a function. For example, run the following query and save it then as a function.

union isfuzzy=true
workspace(“b111d916-5556-4b3c-87cf-f8d93dad7ea0”).SecurityBaseline, workspace(“0a9de77d-650f-4bb1-b12f-9bcdb6fb3652”).SecurityBaseline

We can then call the function in our queries, for example, to get all failed security baseline checks. We don’t need to specify workspaces to join, as they are handled by the function.

ContosoSecEvents
| where ( RuleSeverity == “Critical” )
| where ( AnalyzeResult == “Failed” )
| project Computer, Description

Another way of using saved functions is the following example.
First, we have a saved function named ContosoCompMissingUpdates listing all computers that are missing updates.

union isfuzzy=true
workspace(“b111d916-5556-4b3c-87cf-f8d93dad7ea0”).Update, workspace(“0a9de77d-650f-4bb1-b12f-9bcdb6fb3652”).Update
| where UpdateState == ‘Needed’ and Optional == false and Classification == ‘Security Updates’ and Approved != false
| distinct Computer

We can then use the ContosoCompMissingUpdates function within a query showing machines with failed Security baseline checks. The result is a list of machines missing updates and with failed baseline checks.

ContosoSecEvents
| where ( RuleSeverity == “Critical” )
| where ( AnalyzeResult == “Failed” )
| where Computer in (ContosoCompMissingUpdates)
| project Computer, Description

 

Disclaimer: Cloud is a very fast-moving target. It means that by the time you’re reading this post everything described here could have been changed completely.
Note that this is provided “AS-IS” with no warranties at all. This is not a production-ready solution for your production environment, just an idea, and an example.

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