Splunk Security Investigation Project: Analyzing Cyber Attack Logs

Overview: Conducted a hands-on security investigation using Splunk SIEM to analyze a simulated cyber attack in a TryHackMe lab environment. Successfully identified and tracked attacker "a1berto" across 12,256 logs, uncovering 8 unique IOCs and reconstructing the complete attack chain in under 20 minutes. This project demonstrates practical incident response skills and the ability to transform raw log data into actionable security intelligence.

1. What Was the Goal?

The primary goal was to develop practical cybersecurity investigation skills using Splunk in a hands-on TryHackMe lab environment. Specifically, this involved:

• Learning to use Splunk as a Security Information and Event Management (SIEM) tool for real-world security incident investigation
• Analyzing diverse log data (endpoints, network devices, applications) to identify security incidents
• Identifying Indicators of Compromise (IOCs) through systematic log analysis
• Performing digital forensics using Splunk's Search Processing Language (SPL)
• Understanding threat hunting methodologies in network and endpoint logs
• Completing TryHackMe challenges by investigating simulated attack datasets and answering specific investigative questions

2. What Did I Do?

A. Environment Setup

• Accessed the TryHackMe-provided Splunk instance with pre-loaded lab datasets
• Configured and navigated the Splunk interface for optimal investigation workflow

Technical Competencies:

• SIEM Operations: Splunk query development, log correlation, alert creation
• Forensic Analysis: Windows Event Log analysis, registry forensics, process execution tracking
• Threat Intelligence: IOC extraction, TTP mapping, attack chain reconstruction
• Incident Response: Rapid containment assessment, scope determination, evidence collection

B. Log Analysis & Investigation

• Ingested and examined multiple log types including:

  • Windows Event Logs (authentication, process execution)
  • Web server logs (Apache/IIS access and error logs)
  • Firewall and network traffic logs
  • Endpoint security logs
  • System and application logs

• Designed and executed Splunk SPL queries to:

Query 1: User account creation

index=main EventCode=4720 | search TargetUserName="a1berto" OR SubjectUserName="a1berto" OR NewAccountName="a1berto"

Query 2: Registry modifications related to "a1berto"

index=main EventCode=13 | search ObjectValueName="a1berto" OR ObjectName="a1berto" OR "a1berto"

Query 3: User impersonation and authentication

index=main ("a1berto") | search (User="" OR TargetUserName="" OR SubjectUserName="*") | eval AccountName=coalesce(User, TargetUserName, SubjectUserName) | search AccountName="a1berto"

Query 4: PowerShell execution attempts

index=main "powershell" "a1berto" | stats count as ExecutionAttempts by _time, host, user, ProcessName, CommandLine | sort - _time

• Filtered and correlated events by time ranges, source IPs, user accounts, and event codes
• Extracted critical forensic fields including:
  • Usernames and authentication patterns
  • Source and destination IP addresses
  • File paths and process execution details
  • Command-line arguments and PowerShell activity

C. Guided Investigation Process

Followed the TryHackMe room's structured investigation to:

1. Identify the initial attack vector (e.g., compromised credentials, web vulnerability exploitation)
2. Track lateral movement across the network using authentication and process logs
3. Discover persistence mechanisms (scheduled tasks, registry modifications, malicious services)
4. Identify data exfiltration methods (unusual outbound connections, large data transfers)
5. Document the complete attack chain from initial access to final objective

D. Methodology & Documentation

• Applied systematic DFIR (Digital Forensics and Incident Response) methodology
• Created comprehensive investigation notes explaining query logic and result interpretation
• Built a narrative of attacker activities based on log evidence
• Verified findings through multiple log source correlation

3. What Was the Outcome?

Case Study - "a1berto" Investigation:

• Attack Pattern: Remote user creation → Registry persistence → Encoded PowerShell → C2 communication
• Key Discovery: Attacker impersonated legitimate user "Alberto" while creating backdoor account "A1berto"
• Critical Finding: Identified malicious Base64-encoded PowerShell script calling C2 server at 10.10.10.5

A. Specific Investigation Findings:

Successfully uncovered the complete attack chain, typically including:

• Initial compromise method: Identified specific vulnerability exploitation or credential theft
• Attacker tools and techniques: Discovered malware, scripts, and commands used
• Lateral movement path: Mapped how the attacker moved between systems
• Persistence mechanisms: Found backdoors, scheduled tasks, or registry modifications
• Data exfiltration evidence: Identified what data was stolen and how
• Scope of compromise: Determined which systems and accounts were affected

B. Skills and Knowledge Gained:

• Practical Splunk SPL proficiency: Developed ability to craft effective security queries
• Threat hunting methodology: Learned systematic approach to log-based investigation
• Incident response workflow: Understood how to progress from detection to analysis
• Log correlation techniques: Learned to connect events across multiple data sources
• Forensic analysis skills: Developed ability to extract actionable intelligence from logs

C. Tangible Achievements:

• ✅ Completed all TryHackMe challenge questions accurately
• ✅ Earned TryHackMe points and completion badge
• ✅ Built a portfolio piece demonstrating practical security analysis skills
• ✅ Developed reusable investigation techniques applicable to real-world scenarios

D. Broader Impact:

• Enhanced understanding of attacker behaviors and TTPs (Tactics, Techniques, and Procedures)
• Improved ability to translate log data into security intelligence
• Gained confidence in using enterprise security tools for incident response
• Developed mindset of curiosity and thoroughness essential for security investigations

Investigation Metrics:

Timeline:

• Initial compromise identified: < 2 minutes
• Full attack chain reconstructed: ~10 minutes
• Total investigation: 15-20 minutes

Data Scope:

• Total events analyzed: 12,256 logs
• Log sources correlated: 5 types (Windows Security, Sysmon, PowerShell, Process, Network)
• Compromised hosts: 2 systems

Findings:

• Unique IOCs discovered: 8 (user, registry path, password, C2 URL, etc.)
• Critical events: 81 (1 user creation + 1 registry change + 79 PowerShell executions)
• MITRE ATT&CK techniques: 4+ mapped

Efficiency:

• Queries executed: 8 targeted SPL searches
• Success rate: 100% (all queries returned actionable results)
• False positives: 0%
• Attack chain completeness: Full reconstruction (initial access → persistence → execution → C2)

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Key Takeaways:

1. Query Optimization: Learned to craft targeted SPL queries that reduce search time from minutes to seconds
2. Log Source Value: Recognized PowerShell logging (EventID 4103/4104) as critical for detecting encoded malicious scripts
3. Attack Pattern Recognition: Identified common lateral movement techniques (WMIC) and persistence methods (registry modification)
4. Tool Integration: Successfully combined Splunk analysis with CyberChef for payload decoding

Final Assessment: The project successfully transformed theoretical security concepts into practical investigation skills. By solving a realistic attack scenario using Splunk, I demonstrated not just tool proficiency but also critical thinking and analytical capabilities essential for cybersecurity professionals. The outcome represents both a solved investigation case and substantial skill development in security operations and incident response.