Performing Log Source Onboarding In Siem

Performing Log Source Onboarding in SIEM

Overview

Log source onboarding is the systematic process of integrating new data sources into a SIEM platform to enable security monitoring and detection. Proper onboarding requires planning data sources, configuring collection agents, building parsers, normalizing fields to a common schema, and validating data quality. According to the UK NCSC, onboarding should prioritize log sources that provide the highest security value relative to their ingestion cost.

When to Use

• When conducting security assessments that involve performing log source onboarding in siem
• When following incident response procedures for related security events
• When performing scheduled security testing or auditing activities
• When validating security controls through hands-on testing

Common Misconfigurations & Verification

• Events arrive but fields are unparsed: the source ingests into the index yet props.conf TRANSFORMS/REGEX doesn't match the real log lines, so src_ip, dest_ip, user, action are empty and every correlation search and CIM data model silently misses this source. Verify field-extraction coverage (the count(src_ip)/count query) is near 100%, not just that count by sourcetype is non-zero.
• Timestamp parsing wrong: missing/incorrect TIME_FORMAT, no timezone (%z), or MAX_TIMESTAMP_LOOKAHEAD too short makes Splunk use index time or shift events hours off — alerts fire late, dashboards show gaps, and _time vs _indextime lag balloons. Confirm avg(time_diff) < 300s and that a known event lands at its real wall-clock time.
• CIM tags missing: fields extracted but the sourcetype isn't tagged into the data model (eventtype/tags.conf), so tstats/datamodel searches return nothing. Validate with | datamodel Network_Traffic search | search sourcetype=<new> returning rows.
• Wrong sourcetype/index or duplicate ingest: a default sourcetype (e.g. generic syslog) bypasses your parser, and a forwarder + syslog both shipping the same source double-counts volume and license.
• Verify end to end before closing the ticket: confirm events present, field coverage high, timestamps accurate (_time≈_indextime), CIM compliance via datamodel/tstats, volume within license budget, and that at least one detection rule actually fires on a replayed/known event from the new source.

Prerequisites

• SIEM platform deployed (Splunk, Elastic, Sentinel, QRadar, or similar)
• Network access from source systems to SIEM collectors
• Administrative access on source systems for agent installation
• Common Information Model (CIM) or equivalent schema documentation
• Change management approval for production system modifications

Log Source Priority Framework

Tier 1 - Critical (Onboard First)

Tier 2 - High Priority

Tier 3 - Standard

Onboarding Process

Step 1: Discovery and Assessment

1. Identify the log source:
   - System type and version
   - Log format (syslog, CEF, JSON, Windows Events, etc.)
   - Log volume estimate (EPS - events per second)
   - Network location and firewall requirements

2. Assess security value:
   - What threats can this source help detect?
   - Which MITRE ATT&CK techniques does it cover?
   - Is there an existing SIEM parser?

3. Estimate ingestion cost:
   - Daily volume in GB
   - License impact (per-GB or per-EPS pricing)
   - Storage retention requirements

Step 2: Configure Log Collection

Syslog-Based Collection (Firewalls, Network Devices)

# rsyslog configuration for receiving syslog
# /etc/rsyslog.d/10-siem-collection.conf

# UDP reception
module(load="imudp")
input(type="imudp" port="514" ruleset="siem_forwarding")

# TCP reception
module(load="imtcp")
input(type="imtcp" port="514" ruleset="siem_forwarding")

# TLS reception
module(load="imtcp" StreamDriver.AuthMode="x509/name"
       StreamDriver.Mode="1" StreamDriver.Name="gtls")
input(type="imtcp" port="6514" ruleset="siem_forwarding")

ruleset(name="siem_forwarding") {
    # Forward to SIEM
    action(type="omfwd" target="siem.company.com" port="9514"
           protocol="tcp" queue.type="LinkedList"
           queue.filename="siem_fwd" queue.maxdiskspace="1g"
           queue.saveonshutdown="on" action.resumeRetryCount="-1")
}

Windows Event Log Collection (Splunk Universal Forwarder)

# inputs.conf on Splunk Universal Forwarder
[WinEventLog://Security]
disabled = 0
index = wineventlog
sourcetype = WinEventLog:Security
evt_resolve_ad_obj = 1
checkpointInterval = 5

[WinEventLog://System]
disabled = 0
index = wineventlog
sourcetype = WinEventLog:System

[WinEventLog://Microsoft-Windows-Sysmon/Operational]
disabled = 0
index = wineventlog
sourcetype = XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
renderXml = true

[WinEventLog://Microsoft-Windows-PowerShell/Operational]
disabled = 0
index = wineventlog
sourcetype = XmlWinEventLog:Microsoft-Windows-PowerShell/Operational

Cloud Log Collection (AWS CloudTrail)

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Resources": {
    "CloudTrailToSIEM": {
      "Type": "AWS::CloudTrail::Trail",
      "Properties": {
        "TrailName": "siem-cloudtrail",
        "S3BucketName": "company-cloudtrail-logs",
        "IsLogging": true,
        "IsMultiRegionTrail": true,
        "IncludeGlobalServiceEvents": true,
        "EnableLogFileValidation": true,
        "EventSelectors": [
          {
            "ReadWriteType": "All",
            "IncludeManagementEvents": true,
            "DataResources": [
              {
                "Type": "AWS::S3::Object",
                "Values": ["arn:aws:s3"]
              }
            ]
          }
        ]
      }
    }
  }
}

Step 3: Parse and Normalize

Custom Parser Example (Splunk props.conf/transforms.conf)

# props.conf
[custom:firewall:logs]
SHOULD_LINEMERGE = false
LINE_BREAKER = ([\r\n]+)
TIME_PREFIX = ^
TIME_FORMAT = %Y-%m-%dT%H:%M:%S%z
MAX_TIMESTAMP_LOOKAHEAD = 30
TRANSFORMS-firewall = firewall_extract_fields
FIELDALIAS-src = src_addr AS src_ip
FIELDALIAS-dst = dst_addr AS dest_ip
EVAL-action = case(fw_action=="allow", "allowed", fw_action=="deny", "blocked", true(), "unknown")
EVAL-vendor_product = "Custom Firewall"
LOOKUP-geo = geo_ip_lookup ip AS dest_ip OUTPUT country, city, latitude, longitude

# transforms.conf
[firewall_extract_fields]
REGEX = ^(\S+)\s+(\S+)\s+action=(\w+)\s+src=(\S+):(\d+)\s+dst=(\S+):(\d+)\s+proto=(\w+)\s+bytes=(\d+)
FORMAT = timestamp::$1 hostname::$2 fw_action::$3 src_addr::$4 src_port::$5 dst_addr::$6 dst_port::$7 protocol::$8 bytes::$9

CIM Field Mapping

Step 4: Validate Data Quality

# Verify events are arriving
index=new_source earliest=-1h
| stats count by sourcetype, host, source

# Check field extraction quality
index=new_source earliest=-1h
| stats count(src_ip) as has_src count(dest_ip) as has_dest count(action) as has_action count by sourcetype
| eval src_coverage=round(has_src/count*100,1)
| eval dest_coverage=round(has_dest/count*100,1)
| eval action_coverage=round(has_action/count*100,1)

# Verify CIM compliance
| datamodel Network_Traffic search
| search sourcetype=new_sourcetype
| stats count by source, sourcetype

# Check for timestamp parsing issues
index=new_source earliest=-1h
| eval time_diff=abs(_time - _indextime)
| stats avg(time_diff) as avg_lag max(time_diff) as max_lag by host
| where avg_lag > 300

Step 5: Enable Detection Coverage

# Verify existing correlation searches work with new source
index=new_source sourcetype=new_sourcetype
| tstats count from datamodel=Authentication by _time span=1h
| timechart span=1h count

# Create source-specific detection rule
[New Source - Authentication Anomaly]
search = index=new_source sourcetype=new_sourcetype action=failure \
| stats count by src_ip, user \
| where count > 10

Onboarding Checklist

• Log source assessed and approved
• Network connectivity verified
• Collection agent/method configured
• Log forwarding confirmed
• Parser/field extraction configured
• CIM compliance validated
• Data model acceleration enabled
• Volume within license budget
• Retention policy configured
• Detection rules enabled/created
• Dashboard updated
• Documentation completed
• SOC team notified

References

• UK NCSC - Onboarding Systems and Log Sources
• Sumo Logic - Cloud SIEM Onboarding Checklist
• SIEM Logging Best Practices - Coralogix
• Huntress - SIEM Implementation Guide