analyzing-security-logs-with-splunk

name	analyzing-security-logs-with-splunk
description	Leverages Splunk Enterprise Security and SPL (Search Processing Language) to investigate security incidents through log correlation, timeline reconstruction, and anomaly detection. Covers Windows event logs, firewall logs, proxy logs, and authentication data analysis. Activates for requests involving Splunk investigation, SPL queries, SIEM log analysis, security event correlation, or log-based incident investigation.
domain	cybersecurity
subdomain	incident-response
tags	["splunk","SPL","SIEM","log-analysis","security-monitoring"]
version	1.0.0
author	mahipal
license	Apache-2.0

Analyzing Security Logs with Splunk

When to Use

• Investigating a security incident that requires correlation across multiple log sources
• Hunting for adversary activity using known TTPs and IOCs
• Building detection rules for specific attack patterns
• Reconstructing an incident timeline from disparate log sources
• Analyzing authentication anomalies, lateral movement, or data exfiltration patterns

Do not use for real-time packet-level analysis; use Wireshark or Zeek for full packet capture analysis.

Prerequisites

• Splunk Enterprise or Splunk Cloud with Enterprise Security (ES) app installed
• Log sources ingested: Windows Event Logs (via Splunk Universal Forwarder or WEF), firewall, proxy, DNS, EDR, email gateway
• Splunk CIM (Common Information Model) data models configured for normalized field names
• SPL proficiency at intermediate level or higher
• Role-based access with search and accelerate_search capabilities in Splunk

Workflow

Step 1: Scope the Investigation in Splunk

Define search parameters based on incident triage data:

| Set initial investigation scope
index=windows OR index=firewall OR index=proxy
  earliest="2025-11-14T00:00:00" latest="2025-11-16T00:00:00"
  (host="WKSTN-042" OR src_ip="10.1.5.42" OR user="jsmith")
| stats count by index, sourcetype, host
| sort -count

This query establishes which log sources contain relevant data for the investigation timeframe and affected assets.

Step 2: Analyze Authentication Events

Investigate suspicious authentication patterns using Windows Security Event Logs:

| Detect brute force and credential stuffing
index=windows sourcetype="WinEventLog:Security" EventCode=4625
  earliest=-24h
| stats count as failed_attempts, values(src_ip) as source_ips,
  dc(src_ip) as unique_sources by TargetUserName
| where failed_attempts > 10
| sort -failed_attempts

| Detect pass-the-hash (Logon Type 9 - NewCredentials)
index=windows sourcetype="WinEventLog:Security" EventCode=4624
  Logon_Type=9
| table _time, host, TargetUserName, src_ip, LogonProcessName

| Detect lateral movement via RDP
index=windows sourcetype="WinEventLog:Security" EventCode=4624
  Logon_Type=10
| stats count, values(host) as targets by TargetUserName, src_ip
| where count > 3
| sort -count

Step 3: Trace Process Execution

Use Sysmon logs to reconstruct process execution chains:

| Process creation with parent chain (Sysmon Event ID 1)
index=sysmon EventCode=1 host="WKSTN-042"
  earliest="2025-11-15T14:00:00" latest="2025-11-15T15:00:00"
| table _time, ParentImage, ParentCommandLine, Image, CommandLine, User, Hashes
| sort _time

| Detect suspicious PowerShell execution
index=sysmon EventCode=1 Image="*\\powershell.exe"
  (CommandLine="*-enc*" OR CommandLine="*-encodedcommand*"
   OR CommandLine="*downloadstring*" OR CommandLine="*iex*")
| table _time, host, User, ParentImage, CommandLine
| sort _time

| Detect LSASS credential dumping
index=sysmon EventCode=10 TargetImage="*\\lsass.exe"
  GrantedAccess=0x1010
| table _time, host, SourceImage, SourceUser, GrantedAccess