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Fix the server

Debug challenges: you get a broken server and no instructions. Find the cause and fix it – just like in real operations.

Duration: 45 minLevel: IntermediateExercises: 5

Debug challenge: nginx won't start

Debug challenge: nginx won't start

This lesson is different: you get no instructions, just a broken server. Find out what is wrong and fix it. Try it yourself first – after the first "Check" you get hints in three steps.

The fault is built into your VM when the lesson starts. So start the lesson right here, not from another lesson.

Exercises

  1. 1. Bring the Lab shop back online

    Goal: the Lab shop is reachable again at http://localhost/ and nginx is running – with the repaired shop configuration (not deleted or replaced by another one).

    There are no commands up front. Investigate the server yourself.

Debug challenge: HTTPS does not answer

Debug challenge: HTTPS does not answer

This lesson is different: you get no instructions, just a broken server. Find out what is wrong and fix it. Try it yourself first – after the first "Check" you get hints in three steps.

The fault is built into your VM when the lesson starts. So start the lesson right here, not from another lesson.

Exercises

  1. 1. The shop answers over HTTPS again

    Goal (1/2): on the server itself, https://localhost/ answers with the Lab shop again.

    Find out which port nginx really listens on for HTTPS and fix it in the configuration – no commands up front.

  2. 2. The firewall lets HTTPS through

    Goal (2/2): the firewall stays active and lets HTTPS (port 443) in. SSH must stay allowed.

Debug challenge: the backdoor in cron

Debug challenge: the backdoor in cron

This lesson is different: you get no instructions, just a broken server. Find out what is wrong and fix it. Try it yourself first – after the first "Check" you get hints in three steps.

The fault is built into your VM when the lesson starts. So start the lesson right here, not from another lesson.

Exercises

  1. 1. Find and remove the backdoor

    Goal (1/2): the rule that starts something every minute and the program it starts are removed from the server. The cron service itself keeps running.

    Don't worry: the "malware" is defused in the Lab and makes no real connection.

  2. 2. Make sure it does not come back

    Goal (2/2): the second mechanism that would recreate the backdoor is stopped and does not start again after a reboot either. The cron rule stays gone.

Related courses

nginx TLS HardeningYou harden nginx from an insecure default state (self-signed snakeoil cert + TLSv1 enabled + permissive ciphers + no security headers) into a modern TLS configuration. 7 tasks, about 60 minutes. Note: We use a self-signed certificate — browser warnings are expected here (in production you'd use Let's Encrypt, that's a separate module).Pentest Basics: SSH Brute ForceFirst offensive module: you attack a deliberately weak SSH instance. You'll learn nmap, hydra, and see live why the hardening rules from the SSH-Hardening module are not a toy. Everything happens on YOUR own lab VM (loopback) — no external target.Linux Firewall with nftablesYou learn nftables — the modern successor to iptables, now the default on 75% of Linux servers. You build a production-grade firewall step by step: create tables and chains, allow SSH and HTTP/S, block everything else, and persist your rules. 6 tasks, about 75 minutes.Log Analysis: spot SSH attacks in auth.logThe defender side of the pentest lesson: your VM has 200 synthetic SSH brute-force entries in /var/log/auth.log. With grep, awk and sort you filter out how many failed login attempts there were, which IP is the dominant attacker and how many unique source IPs tried. Four tasks, around 30 minutes. Pure defense — these skills you need every day once a server is live.

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