Arjun Parameter FinderStep-by-step reference: discover hidden HTTP parameters with Arjun. Lab use only.FAQ

What is Arjun?

Arjun is a free, open-source HTTP parameter discovery tool in Python by Somdev Sangwan. It brute-forces GET and POST parameter names from a large built-in list with smart false-positive filtering.

Is using Arjun legal?

Arjun itself is legitimate open-source software. Probing sites without explicit written permission is illegal. Run it only on lab apps or signed targets with modest threads.

How do I install Arjun?

Run pipx install arjun on Python 3.8 or newer. Verify with arjun -h — no keys needed.

How do I find hidden parameters?

Run arjun -u against the authorized URL. Valid hits print with reflection detail — record each for DalFox and SQLMap follow-ups.

How do POST and JSON modes differ?

Default mines query strings; --post tests form bodies and JSON mode probes API payloads. Cover all three where the endpoint accepts them.

Why so many false positives?

Unstable lab responses fool baselines. Re-run with --stable and lower threads until the app answers consistently.

How does Arjun pair with DalFox?

Arjun finds the names, DalFox tests them for XSS. Pipe JSON outputs between the two for a clean discovery-to-exploit chain.

How do developers prevent this?

Allowlist expected parameters, ignore unknown inputs server-side, and validate every value — hidden names must never mean trusted inputs.

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