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31. SOC, SIEM and Incident Response

31.3 What a SIEM Does

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Quick answer: the short, self-contained version of this lesson is the guide What Is SIEM? How SOC Analysts Use It.

Reading logs server by server does not scale. A SIEM (Security Information and Event Management) system:

  1. Collects logs from all servers, firewalls, cloud and applications into one place.
  2. Normalises them into a common format (time, source IP, user, action).
  3. Correlates events with rules, for example "10 failed logins then 1 success from the same IP within 5 minutes".
  4. Alerts analysts and shows dashboards.
  5. Stores logs for investigation and compliance.

Popular options:

Tool Type Notes
Splunk Commercial (free trial / limited free version) Very common in large companies; search language SPL
Microsoft Sentinel Cloud SIEM (Azure) Common where companies use Microsoft 365/Azure
ELK / Elastic Stack Open source core (Elasticsearch, Logstash/Beats, Kibana) Flexible; Elastic Security adds detection rules
Wazuh Free and open source SIEM plus host agent: log analysis, file integrity, vulnerability detection; great for labs
QRadar, ArcSight Commercial Seen in banks and older enterprises

A sample Splunk search (SPL) that an analyst might run:

index=linux sourcetype=linux_secure "Failed password"
| stats count by src_ip
| where count > 20
| sort - count

Related tools you will meet: EDR (Endpoint Detection and Response, for example CrowdStrike, Microsoft Defender for Endpoint) watches processes on each machine; SOAR automates response steps (block IP, disable user) from playbooks; IDS/IPS such as Snort and Suricata (Chapter 32) watch network traffic.

Ravindra Bagale's Tip

If an interviewer asks "Do you know Splunk?" and you have never used Splunk, don't panic. The concept of a SIEM (collect, correlate, alert) is the same. If you did Wazuh in the lab and can explain it, interviewers like that even more. Talk about what you have actually done.

Practice task

Write a correlation rule in plain English for each: (1) SSH brute force followed by success, (2) a new IAM user created at 2 a.m. in AWS, (3) one IP requesting more than 200 different URLs in one minute. Name the log source each rule needs.

Extended teaching notes

Why this lesson matters

A SOC turns logs into action. Good juniors triage with playbooks: what fired, which asset, how bad, contain or escalate, write the timeline.

  1. Prepare: asset list, contacts, runbooks.
  2. Detect: SIEM/EDR alerts with context.
  3. Contain: disable account, isolate host, block IOC.
  4. Eradicate & recover: patch, rebuild, restore.
  5. Lessons: one improvement ticket per incident.

Indian company (sample)

A 24×7 SOC at a large Indian IT services firm handles phishing and malware for many clients. Tier-1 analysts follow a script; they do not freestyle on production.

Mini case study

Suppose we are on a purple-team exercise for an Indian mid-size company (sample data). Red notes a technique from this lesson against a lab clone. Blue must show the control that stops it, the log that would have fired, and the ticket that hardens production. That is the standard this course trains you for.

Defender's worksheet (do this today)

  1. Write the lesson title, date and the exact lab target you are allowed to use.
  2. List three owned systems (VMs, apps, or cloud accounts) where this lesson applies.
  3. Run one safe check from the lesson on a lab system only. Paste the command and output.
  4. Write a two-sentence fix you would give a teammate.
  5. Name one related public advisory (CERT-In, CISA, NVD, or a vendor bulletin) with its date.

Indian workplace (sample data)

Suppose we are a junior analyst at Infosys, TCS, Wipro or a fintech SOC in Bengaluru/Pune. Turn this lesson into one checklist item with an owner, a due date and a place to store evidence (ticket + screenshot).

Global practice

Compare your notes with OWASP, CIS Benchmarks, NIST CSF/IR guidance or a cloud Well-Architected security question. Write five lines on what overlaps.

Everyday analogy

Explain the risk and the fix to a family member without jargon. If they can repeat the warning, you understand it well enough to teach juniors.

Key terms

  • Control: a safeguard (patch, config, process, detection).
  • Finding: a weakness backed by evidence.
  • Remediation: the fix plus how you verified it.
  • Scope: systems you have written permission to touch.
  • Least privilege: only the access the task needs.
  • Defence in depth: several layers so one failure does not end the story.

Common mistakes

  • Skipping written permission "just for a quick scan".
  • Practising on hostel, office or public targets without authorisation.
  • Collecting tool output without writing the fix.
  • Copying attack steps onto production to "verify". Defenders verify with versions, configs and patches.
  • Publishing screenshots that contain secrets, cookies or internal hostnames.

Recap

  • Evidence, fix, owner, date.
  • Own lab only.
  • Fix > spectacle.