Getting it into your agent
It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.
git clone --depth 1 https://github.com/forefy/.contextnpx agentmods add skills/forefy/.context/jwt-attacksWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/forefy/.context/jwt-attacks)<a href="https://agentmods.dev/skills/forefy/.context/jwt-attacks"><img src="https://agentmods.dev/badge/skills/forefy/.context/jwt-attacks/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/forefy/.context/jwt-attacks"><img src="https://agentmods.dev/badge/skills/forefy/.context/jwt-attacks.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 5 findings, up to high
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- high Privilege Escalation · line 38 Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
- high Privilege Escalation · line 40 Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
- high Privilege Escalation · line 109 Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
- high Privilege Escalation · line 112 Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
- high YARA Match · line 38 YARA rule matched a hack tool or exploit indicator (offensive tools, reconnaissance, privilege escalation, or exploit frameworks).Fix: Remove offensive tool references and exploit code. Legitimate agent skills should not contain penetration testing tools, exploit frameworks, or reconnaissance utilities.
What 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 5.1 | $0.00044 | $0.03279 |
| Opus 5.5 | $0.00018 | $0.01312 |
| Sonnet 5.5 | $0.00009 | $0.00656 |
| Haiku 4.5 | $0.00004 | $0.00328 |
Grade A, and why
jwt-attacks 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 1mo ago.
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.
curl -sk -o /dev/null -w '%{http_code}\n' \ How it starts
The opening of the file, as written. The whole thing — 194 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Contents
- Scope & authorization
- Step 0 - locate the token and establish a baseline
- Step 1 - offline HMAC secret crack (passive)
- Step 2 - signature stripping (active)
- Step 3 - alg:none family (active)
- Step 4 - kid manipulation (active)
- Step 5 - self-signed key injection: jwk / jku (active)
- Step 6 - RS256->HS256 algorithm confusion (active)
- Runnable snippets
- Output
Scope & authorization
Only run against an application you own or are engaged to test. The offline secret-cracking step (Step 1) is fully passive - it only analyzes a token you already captured and makes no network requests, so it is always safe to run. Every forgery step after it is active: it replays a tampered token against the live server, which mutates the authenticated session and appears in the target's logs. Do not run the active steps against third-party or out-of-scope hosts.
Inputs are the JWTs you already hold - captured from proxy history, a browser session, or an Authorization header the app issued to you. Outputs are "report a finding when the server accepts a token you forged."
Step 0 - locate the token and establish a baseline
- Find the JWT. In each captured request, read the
Authorizationheader. Strip a leadingBearerif present. A JWT is three base64url segments joined by dots (header.payload.signature) and the header segment almost always starts withey(that is{"base64url-encoded). Tokens also appear in cookies and inaccess_token/id_tokenbody or query params - check those too. Skip any auth header whose value does not start withey; after ~3 non-JWT auth values on a host, move on. - Decode it (passive). base64url-decode segment 1 (header) and segment 2 (payload). Note
alg,kid,jku,jwkin the header andexp,iat, roles/scopes/subin the payload - these drive both the crack and the forgeries. - Establish the rejection baseline (active). Before forging anything, confirm the endpoint actually enforces the token: replay the request with a deliberately invalid token (original token with its last signature character changed) and confirm the server answers
401 Unauthorized. Only endpoints that reject a bad token are worth attacking - if an endpoint returns 200 for garbage, it never checked the token and the "forgery accepted" signal is meaningless. Rate-limit yourself: after ~5 filtered requests that fail to return 401 to an invalid token, stop on that host.
What ships with it
1 file 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.
- 1mo ago Changed · +2 lines 4e6e788c5f34
- 1mo ago Changed · +1 lines 0366051b0649
- 1mo ago First seen · 191 lines · 44 tokens per session scan A ccb70f03d7fe
jwt-attacks is a skill published in the GitHub repository forefy/.context (153 stars, last pushed yesterday), licensed MIT. It adds 44 tokens to every session and 3,279 once invoked, about $0.0002 per session on Opus 5.5. 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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