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Log Priority

The following is a prioritized list of recommended event logs to collect into your SIEM (ordering should be customized per organization and is subject to change here).

  • Security Product Logs (EDR/AV/HIPS/IPS)
  • Windows DC Event Logs / LDAP Logs
  • Web Proxy Requests
  • PowerShell Logs
  • DNS Queries (with endpoint name/IP)
  • Firewall (Egress Only)
  • VPN Logs
  • Google Cloud Logging
  • AWS CloudWatch
  • Microsoft M365 UnifiedAuditLog
  • Microsoft AzureAD Sign-In Logs
  • Microsoft Cloud App Security Logs
  • Microsoft AzureAD Identity Protection
  • Microsoft M365 Defender for Identity
  • Linux osquery Logs
  • Windows Member Server Event Logs
  • Windows Workstation Event Logs
  • Linux auditd Logs
  • Email Logs
  • Custom Application Logs
  • Firewall
  • DHCP
  • Netflow
  • AWS VPC Flow Logs
  • Google VPC Flow Logs
  • Microsoft Network Security Group Flow Logs
  • Full packet capture

The priority here takes into consideration

  • Data ingestion/space restrictions
  • Common attack vectors
  • Common detection sources
  • Expected noise levels
  • Overaid aid to investigations
  • Legal precedence on what adequate security monitoring includes

Requirements

  • Normalize all field names and content. This is critical to success in correlation and analyst faith in their search results.
  • Parse-out nested fields. Looking at you, Microsoft Event Log "Message" field.
  • All event logs should be set to ISO 8601 UTC. This may require transforms to convert from the original device's local time.
  • All devices should sync with Network Time Protocol (NTP) providers.

Considerations

  • What in the system performance impact of log collection on an endpoint?
  • What in the system performance impact of log collection on network appliances?
  • How long should data be held in "hot" (searchable) storage?
  • How long is data to be held in "cold" (backup) storage?
  • How much storage space is needed?
  • Is there an enforceable logging policy in place?
  • What is the expected event load on the server, and what is the appropriate amount of hardware resources to handle the load?
  • How will event log feeds be monitored for issues/outage?
  • What is the maximum allowable travel time from when an event occurs to when the log reaches the centralized logging server?

Event Reduction

Reduction of ingested events to only those with a security concern is highly recommended. This may require a separate 'data lake' from logs maintained for regulatory compliance. Reduced logs saves money, analyst time, and improves system performance.

Common tune-outs at the ingest level include

  • Authorized vulnerability scanners
  • Debug logs
  • Encrypted data
  • File access by backup service accounts
  • Common application errors
  • Health Checks

Some logs can be significantly reduced by eliminating one or more fields, like Windows Event Logs often multi-paragraph long descriptions included in the log.

Logs that do not provide basic security context should be considered for tuning out:

  • Date and Time of Action
  • Source System/Account Attribution
  • Description of Action
  • Description of Target (when applicable)
  • Description of Outcome (sometimes implied)

Note: This does not immply that non-security focused logs are of no value/use.

Detection Layering

This approach allows a high-level understanding of interactions between log collection, detections, and monitoring.

  • Detection can (and should) occur at any tier.
  • "Tuning" based on content analysis and feedback should be used on every tier.

Tiers

  • Raw Events

    • Monitoring for visible anomalies in a stream of events.
      • Are the logs needed?
      • Can we filter some events?
      • Are the appropriate fields collected?
      • Are the fields parsed correctly?

  • Aggregation of Raw Events (usually via widgets on dashboards)

    • Stack counting of one or more fields helps surface interesting events
    • Which fields do you aggregate?
    • When should information roll over/expire?
    • Styles
    • Aggregation counts
      • First occurance
      • Last occurance
      • Frequency bar chart enabling Long tail analysis

  • Prioritized Alerts

    • When confirmed incidents are found, an opportunity to create a prioritized alert is presented.
      • What is the criticality of asset? - People - Services - Devices - Data
        • Tiers within assets
        • Interaction between assets
      • What is the fidelity of the technique?
        • Blacklist Alert
        • Whitelist
        • Count Threshold
        • Newly Observed
        • Etc.

  • Incidents

    • A Prioritized Alert of highest severity requires acknowledgement.
    • Known-Bad
      • Vendor Signature
      • IP
      • Domain
      • Etc.

Log Setup

PowerShell Transcription

https://devblogs.microsoft.com/powershell/powershell-the-blue-team/

  • Set up PowerShell Transcription logging via GPO at
    • Windows Components -> Administrative Templates -> Windows PowerShell
  • Turn On PowerShell Transcription: ON
    • Set Transcript output directory to the \server\transcripts share path
    • Check Include Invocation Headers

Windows Event Forwarding and Collector

https://docs.microsoft.com/en-us/windows/security/threat-protection/use-windows-event-forwarding-to-assist-in-intrusion-detection https://docs.microsoft.com/en-us/windows/win32/wec/windows-event-collector https://medium.com/palantir/windows-event-forwarding-for-network-defense-cb208d5ff86f https://hackernoon.com/the-windows-event-forwarding-survival-guide-2010db7a68c4 http://zenshaze.com/wp/?p=57

  • Set WEC timezone to UTC / GMT
  • Set up GPO Computer Configuration → Policies → Administrative Templates → Windows Components → Event Forwarding → Configure Target Subscription Manager
  • Set up subscriptions