Defense & IR · easy · solved in-browser (no VM needed) · 3 tiered hints
Write /etc/hosts.deny to contain a brute-forcer. Deny sshd access from the single host 203.0.113.7, deny all services from the subnet 198.51.100.0/24, and add a final catch-all line that denies ALL services from ALL hosts (the default-deny posture, relying on /etc/hosts.allow for exceptions). (Authored config, graded structurally — the engine isn't run here.)
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Open the challenge and an in-page editor appears — write your answer and tmpfs.tech grades it server-side against the same checks a real box would run. No VM, no install, no signup needed to try.
Incident response: evict rogue accounts, eradicate persistence, attribute a breach.
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