Performing Log Analysis for Forensic Investigation

When to Use

• When reconstructing the timeline of a security incident from available log sources
• During post-breach investigation to identify initial access, lateral movement, and exfiltration
• When correlating events across multiple systems and log sources
• For establishing evidence of unauthorized access or policy violations
• When preparing forensic reports requiring detailed event chronology

Prerequisites

• Access to collected log files (Windows Event Logs, syslog, application logs)
• Log parsing tools (LogParser, jq, awk, or ELK stack)
• Understanding of log formats (EVTX, syslog, JSON, CSV)
• NTP-synchronized timestamps across all log sources for correlation
• Sufficient storage for log aggregation and indexing
• Timeline analysis tools (log2timeline, Plaso)

Workflow

Step 1: Collect and Preserve Log Sources

# Create case log directory structure
mkdir -p /cases/case-2024-001/logs/{windows,linux,network,application,web}

# Extract Windows Event Logs from forensic image
cp /mnt/evidence/Windows/System32/winevt/Logs/*.evtx /cases/case-2024-001/logs/windows/

# Key Windows Event Logs to collect
# Security.evtx - Authentication, access control, policy changes
# System.evtx - Service starts/stops, driver loads, system errors
# Application.evtx - Application errors and events
# Microsoft-Windows-PowerShell%4Operational.evtx - PowerShell execution
# Microsoft-Windows-Sysmon%4Operational.evtx - Sysmon detailed events
# Microsoft-Windows-TaskScheduler%4Operational.evtx - Scheduled tasks
# Microsoft-Windows-TerminalServices-LocalSessionManager%4Operational.evtx - RDP

# Collect Linux logs
cp /mnt/evidence/var/log/auth.log* /cases/case-2024-001/logs/linux/
cp /mnt/evidence/var/log/syslog* /cases/case-2024-001/logs/linux/
cp /mnt/evidence/var/log/kern.log* /cases/case-2024-001/logs/linux/
cp /mnt/evidence/var/log/secure* /cases/case-2024-001/logs/linux/
cp /mnt/evidence/var/log/audit/audit.log* /cases/case-2024-001/logs/linux/

# Collect web server logs
cp /mnt/evidence/var/log/apache2/access.log* /cases/case-2024-001/logs/web/
cp /mnt/evidence/var/log/nginx/access.log* /cases/case-2024-001/logs/web/

# Hash all collected logs for integrity
find /cases/case-2024-001/logs/ -type f -exec sha256sum {} \; > /cases/case-2024-001/logs/log_hashes.txt

Step 2: Parse Windows Event Logs

# Install python-evtx for EVTX parsing
pip install python-evtx

# Convert EVTX to XML/JSON for analysis
python3 -c "
import Evtx.Evtx as evtx
import json, xml.etree.ElementTree as ET

with evtx.Evtx('/cases/case-2024-001/logs/windows/Security.evtx') as log:
    for record in log.records():
        print(record.xml())
" > /cases/case-2024-001/logs/windows/Security_parsed.xml

# Using evtxexport (libevtx-utils)
sudo apt-get install libevtx-utils
evtxexport /cases/case-2024-001/logs/windows/Security.evtx \
   > /cases/case-2024-001/logs/windows/Security_exported.txt

# Key Security Event IDs to investigate
# 4624 - Successful logon
# 4625 - Failed logon
# 4648 - Logon using explicit credentials (runas, lateral movement)
# 4672 - Special privileges assigned (admin logon)
# 4688 - Process creation (with command line if auditing enabled)
# 4697 - Service installed
# 4698/4702 - Scheduled task created/updated
# 4720 - User account created
# 4732 - Member added to security-enabled local group
# 1102 - Audit log cleared

# Extract specific events with python-evtx
python3 << 'PYEOF'
import Evtx.Evtx as evtx
import xml.etree.ElementTree as ET

target_events = ['4624', '4625', '4648', '4672', '4688', '4697', '1102']

with evtx.Evtx('/cases/case-2024-001/logs/windows/Security.evtx') as log:
    for record in log.records():
        root = ET.fromstring(record.xml())
        ns = {'ns': 'http://schemas.microsoft.com/win/2004/08/events/event'}
        event_id = root.find('.//ns:EventID', ns).text
        if event_id in target_events:
            time = root.find('.//ns:TimeCreated', ns).get('SystemTime')
            print(f"[{time}] EventID: {event_id}")
            for data in root.findall('.//ns:Data', ns):
                print(f"  {data.get('Name')}: {data.text}")
            print()
PYEOF

Step 3: Parse and Analyze Linux/Syslog Entries

# Parse auth.log for SSH and sudo events
grep -E '(sshd|sudo|su\[|passwd|useradd|usermod)' \
   /cases/case-2024-001/logs/linux/auth.log* | \
   sort > /cases/case-2024-001/analysis/auth_events.txt


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