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31. SOC, SIEM and Incident Response

31.5 Alert Triage

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In short: Triage means quickly deciding what each alert is and what to do next.

Quick answer: the short, self-contained version of this lesson is the guide MITRE ATT&CK + Your First Sigma Detection Rule (Defence).

Triage means quickly deciding what each alert is and what to do next.

Outcome Meaning Example
True positive Real attack, alert is correct Brute force followed by successful login from an unknown foreign IP
False positive Alert fired but nothing bad happened Admin mistyped their password five times
True negative No alert, nothing bad Normal traffic
False negative Attack happened but no alert – the most dangerous Attacker used a valid stolen password during office hours

An L1 triage routine for every alert:

  1. Read the alert: what rule, which host, which user, which source IP, what time.
  2. Enrich: is the IP internal or external? Check reputation on services like AbuseIPDB or VirusTotal. Is the user real and expected on this host?
  3. Scope: did the same IP or user touch other hosts? Any success after the failures?
  4. Decide: false positive (close with a note), or true positive (escalate to L2 with evidence).
  5. Document everything in the ticket: what you checked, what you found, why you decided.

Severity usually considers impact (production server, customer data) and confidence. A failed scan against a patched web server is low; an admin login from a new country followed by a new user being created is critical.

Ravindra Bagale's Tip

Writing only "false positive – closed" in a ticket is the most common L1 mistake. Write why it is a false positive: "User Sneha entered the wrong password 5 times over VPN, then logged in with the correct password; the IP belongs to the company." This is very useful for the next shift and for audits.

Practice task

For each alert, decide true or false positive and write a one-line ticket note: (1) 40 failed SSH logins from an external IP, no success; (2) 5 failed logins then success for user admin from a new country at 3 a.m.; (3) Nikto scan alert from the company's own vulnerability scanner IP during an approved scan window.

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.