/12-log-analysis

name: Log Analysis & SIEM Integration
description: Security log parsing, anomaly detection, SIEM query building, Sigma rule creation, and correlation rule development across Splunk, Elastic, QRadar, and Microsoft Sentinel
version: 3.1.0
author: Masriyan
tags: [cybersecurity, log-analysis, siem, splunk, elastic, sentinel, sigma, anomaly-detection, correlation]

Log Analysis & SIEM Integration

Purpose

Enable Claude to assist with security log analysis across all major platforms. Claude directly parses and analyzes log samples provided by the user, builds SIEM queries for any platform, creates Sigma rules for portable detection, develops correlation rules, and identifies anomalous patterns in log data.

---

Activation Triggers

This skill activates when the user asks about:

• Parsing Windows Event Logs, Linux syslog, or application logs
• Building Splunk SPL, Elastic KQL/EQL, QRadar AQL, or Sentinel KQL queries
• Creating Sigma rules for platform-agnostic detection
• Detecting anomalies or attack patterns in log data
• Building SIEM correlation rules for complex attack scenarios
• Converting queries between SIEM platforms
• Log source health monitoring and gap analysis
• Detecting lateral movement, privilege escalation, or persistence in logs
• EVTX analysis or Windows audit log review

---

Prerequisites

pip install pandas pyyaml python-dateutil

**Platform tools:**

• `Splunk` — Splunk Web, SPL, and SOAR
• `Elastic Stack` — Kibana, KQL, EQL
• `Microsoft Sentinel` — KQL, Workbooks
• `IBM QRadar` — AQL, Rules
• `Sigma` — Platform-agnostic rule format
• `python-evtx` — Parse Windows .evtx files without Windows

---

Core Capabilities

1. Log Parsing & Analysis

**When the user pastes logs or provides log files:**

Claude directly reads and analyzes logs to extract security-relevant events.

**Windows Event Log — Critical Event IDs:**

| Event ID | Log | Description | |----------|-----|-------------| | 4624 | Security | Successful logon — Logon Type 3 (network) is interesting | | 4625 | Security | Failed logon — track source IP for brute force | | 4648 | Security | Logon with explicit credentials (RunAs) | | 4688 | Security | New process created — needs CommandLine auditing enabled | | 4698 | Security | Scheduled task created | | 4702 | Security | Scheduled task updated | | 4720 | Security | User account created | | 4728/4732 | Security | Member added to security/local group | | 4768/4769 | Security | Kerberos TGT/TGS requested | | 4776 | Security | NTLM authentication | | 4946 | Security | Windows Firewall rule added | | 5140 | Security | Network share accessed | | 5145 | Security | Network share file access | | 7045 | System | New service installed | | 1102 | Security | Audit log cleared | | 4103/4104 | PowerShell | PowerShell module/script block logging |

**Linux Log Analysis — Key Patterns:**

# Failed SSH logins
grep "Failed password" /var/log/auth.log | awk '{print $1,$2,$3,$11}' | sort | uniq -c | sort -rn

# Successful logins after failures (brute force success)
grep "Accepted password\|Accepted publickey" /var/log/auth.log

# Sudo usage
grep "sudo:" /var/log/auth.log | grep -v "session"

# Cron job execution
grep CRON /var/log/syslog

# New user creation
grep "useradd\|usermod" /var/log/auth.log

# Privilege escalation
grep "su\b" /var/log/auth.log

**Log parsing script:**

python scripts/log_parser.py --input /var/log/auth.log --format json --output parsed.json
python scripts/log_parser.py --input events.evtx --normalize ecs --output normalized.json

2. SIEM Query Library

**When the user asks to build detection queries:**

Splunk SPL — Attack Pattern Queries

// Brute force attack detection
index=windows EventCode=4625
| bin _time span=5m
| stats count as FailedLogins, values(Account_Name) as Accounts by src_ip, _time
| where FailedLogins > 20
| sort -FailedLogins

// Pass-the-Hash detection (Logon Type 3 with NTLM)
index=windows EventCode=4624 Logon_Type=3 Authentication_Package=NTLM
| where NOT (Account_Name="ANONYMOUS LOGON" OR Account_Name="*$")
| stats count by Account_Name, Workstation_Name, src_ip
| where count > 1

// Lateral movement via PsExec / admin shares
index=windows EventCode=5145
| where (ShareName="\\\\*\\ADMIN$" OR ShareName="\\\\*\\C$") 
    AND RelativeTargetName="*PSEXESVC*"
| table _time, SubjectUserName, IpAddress, ShareName

// PowerShell encoded command execution
index=windows (source="WinEventLog:Microsoft-Windows-PowerShell/Operational" EventCode=4104)
    OR (EventCode=4688 CommandLine="*powershell*")
| search CommandLine IN ("*-EncodedCommand*", "*-enc *", "*-e *", "*-nop*", 
                          "*DownloadString*", "*IEX*", "*Invoke-Expression*")
| table _time, ComputerName, User, CommandLine

// Scheduled task creation for persistence
index=windows EventCode=4698
| rex field=TaskContent "<Command>(?P<command>[^<]+)</Command>"
| where NOT match(command, "(?i)\\\\windows\\\\|\\\\microsoft\\\\|\\\\system32\\\\")
| table _time, ComputerName, SubjectUserName, TaskName, command

// LSASS memory access (credential dumping)
index=sysmon EventCode=10 TargetImage="*lsass.exe"
| where NOT (SourceImage IN 
    ("C:\\Windows\\System32\\*", "C:\\Windows\\SysWOW64\\*",
     "C:\\Program Files\\*", "C:\\Program Files (x86)\\*"))
| table _time, SourceImage, GrantedAccess, CallTrace

// DCSync detection
index=windows EventCode=4662 
    (ObjectType="*domainDNS*" OR ObjectType="*19195a5b-6da0-11d0-afd3-00c04fd930c9*")
    (Properties="*Replicating Directory Changes All*" OR Properties="*1131f6ad*")
| where NOT match(SubjectUserName, "(?i)^.*\$$") 
| table _time, SubjectUserName, SubjectDomainName, Properties

// Kerberoasting detection
index=windows EventCode=4769 Ticket_Encryption_Type=0x17
| where NOT (Account_Name="*$" OR Service_Name IN ("krbtgt", "kadmin/changepw"))
| stats count by Account_Name, Client_Address, Service_Name
| where count > 3

Microsoft Sentinel KQL — Que