Exchange OAB Virtual Directory Attribute Containing Potential Webshell

Original query, unchanged.

SecurityEvent
// Look for specific Directory Service Changes and parse data
| where EventID == 5136
| extend EventData = parse_xml(EventData).EventData.Data
| mv-expand bagexpansion = array EventData
| evaluate bag_unpack(EventData)
| extend Key = tostring(column_ifexists('@Name', "")), Value = column_ifexists('#text', "")
| evaluate pivot(Key, any(Value),TimeGenerated, EventID, Computer, Account, AccountType, EventSourceName, Activity, SubjectAccount)
// Where changes relate to Exchange OAB
| extend ObjectClass = column_ifexists("ObjectClass", "")
| where ObjectClass =~ "msExchOABVirtualDirectory"
// Look for InternalHostName or ExternalHostName properties being changed
| extend AttributeLDAPDisplayName = column_ifexists("AttributeLDAPDisplayName", "")
| where AttributeLDAPDisplayName in~ ("msExchExternalHostName", "msExchInternalHostName")
// Look for suspected webshell activity
| extend AttributeValue = column_ifexists("AttributeValue", "")
| where AttributeValue has "script"
| project-rename LastSeen = TimeGenerated
| extend ObjectDN = column_ifexists("ObjectDN", "")
| project-reorder LastSeen, Computer, Account, ObjectDN, AttributeLDAPDisplayName, AttributeValue
| extend timestamp = LastSeen
| extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
| extend AccountName = tostring(split(Account, @'\')[1]), AccountNTDomain = tostring(split(Account, @'\')[0])