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40. DoS and DDoS – Availability Attacks

40.4 Amplification and Reflection – Closed Lab Only

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Reflection: attacker spoofs victim IP as source; open server replies to the victim. Amplification (प्रवर्धन): tiny query → huge response (DNS, NTP, Memcached historically abused when mis-exposed).

Public lesson (GitHub 2018 era): Memcached UDP on internet + spoofing = enormous reflected flood. You must NEVER scan public Memcached/NTP/DNS for amp, NEVER spoof against third parties.

Blue hygiene:

  • Do not expose Memcached / open recursive DNS / insecure NTP to the whole internet
  • UDP services bind to private IPs / VPC only
  • Providers filter spoofed egress (BCP38 theme)
Red team (attacker) does Blue team (defender) detects / stops
Spoofs victim IP; queries open amplifiers Anti-spoof egress; shut open resolvers; block UDP 11211 inbound from internet
Hopes SME leaves lab Memcached on 0.0.0.0:11211 Security group / firewalld: private only; ss -ulnp audit
Uses amp for "anonymous" volume Scrubbing centre recognises amp signatures; source is reflected servers

Ravindra Bagale's Tip

Students say "let me try Memcached amplification in the lab" and leave the network bridged – a neighbour's PC will get hit too. Amplification demos, if the trainer allows them, only on an air-gapped / host-only pair of VMs. Default advice: study theory + GitHub postmortem, don't build amp. Now let's move on.

Practice task

Write 10-line hardening note for fictional Raja-Rani Traders: list UDP services they run (DNS internal? Memcached for PHP?). For each: bind address, firewall rule, "internet-facing? NO". Cite why GitHub-class amp matters to SMEs who accidentally expose cache.

Real incident: GitHub Memcached DDoS (2018)

On 28 February 2018, GitHub reported a memcached UDP amplification DDoS that peaked at a reported 1.35 Tbps and about 126.9 million packets per second, originating across many ASNs and endpoints. GitHub mitigated by shifting traffic to Akamai Prolexic scrubbing. Weakness theme: memcached instances reachable on the public internet with UDP enabled; spoofed queries produce huge replies toward the victim. Defence: never expose memcached to the internet; UDP service lockdown; scrubbing / Anycast capacity. Source: GitHub Blog "February 28th DDoS Incident Report" (verify).

Extended teaching notes

Why this lesson matters

Availability attacks try to exhaust bandwidth, connections or app workers. Learning them is about detection and defence — never about stressing networks you do not own (that can be illegal and harmful).

  • Rate limits and WAF/CDN at the edge.
  • SYN cookies / tuning on servers.
  • Autoscaling with care (cost controls).
  • Keep IoT devices off default passwords (Mirai lesson).
  • Lab simulations only on isolated networks you own.

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.