Offensive Lab · easy · solved in-browser (no VM needed) · 3 tiered hints
Your own disposable practice box. /usr/bin/base64 is installed SUID-root, so it can read files only root may read. Because base64 itself cannot print plaintext, the trick is to base64-encode the protected file as root and decode the result back to plaintext. Write /home/player/ans.txt with a single pipeline that runs base64 on /root/flag.txt, pipes the encoded output to base64 with a decode flag (-d or --decode), and redirects the recovered plaintext into /home/player/flag. (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.
Authorized local-privilege-escalation wargames on a disposable box you own.
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Is it free? Yes — play as a guest, no signup required to start.
Do I need to install anything? No. Everything runs in your browser.
How is it graded? Automatically and deterministically — your work is checked against the exact rules the live box would apply.