> ## Documentation Index
> Fetch the complete documentation index at: https://community.rifteo.com/llms.txt
> Use this file to discover all available pages before exploring further.
# JWT Cracker
> Full JWT attack methodology alg:none, RS256 to HS256 confusion, weak secret brute-force, kid injection, jku/jwk injection, and claim tampering. Trigger when the user asks to test JWT tokens, authentication bypass, or token forgery, wants to try alg:none/algorithm confusion/weak secret brute-force, needs to test kid/jku/x5u/jwk injection, asks to check if exp/iss/aud claims are validated, is trying to bypass authentication on an API or web app, or provides a string that looks like a JWT.
**Status:** Stable
**Version:** 1.0.0
**Author:** Rifteo
**Tags:** pentest, security, access
**Installation**
```bash theme={"system"}
rifteo-skills add jwt-cracker
```
***
## Summary
Work through a complete 11-attack JWT exploitation methodology from decoding the token to forging one with admin claims covering every known attack class against HMAC and asymmetric JWT implementations.
* Decodes and inspects the header (`alg`, `kid`, `jku`, `x5u`, `jwk`) to select the highest-impact attacks first
* Covers `alg:none`, RS256 → HS256 algorithm confusion, weak HMAC secret brute-force, `kid` SQL injection, `kid` path traversal, `jku`/`x5u` header injection, and embedded `jwk` injection
* Tests claim validation issues: expired token acceptance, missing `iss`/`aud` validation, and cross-service token relay
* Includes ready-to-run Python snippets and `jwt_tool` shortcuts for each attack
***
## SKILL.md file
### JWT Cracker
Execute a structured JWT attack sequence against a target, working from token decode through signature bypass and claim tampering.
#### What Does It Check?
JWT vulnerabilities occur when the server accepts a token it should reject because the signature check is weak, skipped, or bypassable. The skill decodes the token header, identifies the algorithm and any key-reference fields, then selects and executes the relevant attacks in priority order.
**In scope:**
* All HMAC algorithms: HS256, HS384, HS512
* Asymmetric algorithms: RS256, ES256
* All JWT header fields: `alg`, `kid`, `jku`, `x5u`, `jwk`
* Claim validation: `exp`, `iss`, `aud`, `sub`, `role`, `org_id`
* Cross-service token relay (shared key without `aud` validation)
**Out of scope:**
* OAuth 2.0 flows (authorization code, PKCE) JWT signing is only one component
* Refresh token attacks separate class of vulnerability
#### How It Works
**Pre-attack: Decode the Token**
Split the JWT and base64url-decode the header and payload to read `alg`, `kid`, `jku`, `x5u`, and `jwk` fields. These drive which attacks to try first.
**Attack 1: `alg:none`**
Set the header algorithm to `"none"` (and all case variants: `None`, `NONE`, `nOnE`) and strip the signature. If the server accepts it, full token forgery is confirmed.
**Attack 2: RS256 → HS256 Algorithm Confusion**
If `alg: RS256`, obtain the public key from `/.well-known/jwks.json` or similar endpoints. Re-sign the token using HS256 with the PEM-encoded public key as the HMAC secret.
**Attack 3: Weak HMAC Secret Brute-Force**
Run the full JWT against `hashcat` (GPU), `john`, or `jwt_tool -C` using common defaults and the bundled `references/jwt-secrets.txt` wordlist.
**Attack 4: `kid` SQL Injection**
If a `kid` field is present, inject a UNION SELECT payload to make the database return a known value as the signing key, then sign the token with that value.
**Attack 5: `kid` Path Traversal**
Point `kid` to `/dev/null` or a file with known content (e.g. `../../public/logo.png`) and sign with that file's content as the HMAC secret.
**Attack 6: `jku` / `x5u` Header Injection**
Generate a key pair, host the JWKS at an attacker-controlled URL, inject that URL into `jku`, and sign the token with the private key.
**Attack 7: Embedded `jwk` Injection**
Inject a self-generated key pair as the `jwk` header field and sign the token with the corresponding private key.
**Attacks 8–11: Claim and Validation Checks**
After any successful forgery: tamper with `sub`, `role`, `is_admin`, `org_id`, and privilege-related claims. Also test expired token acceptance, missing `iss`/`aud` validation, and cross-service token relay.
#### Output
| Status | Condition |
| ------------------- | -------------------------------------------------------------- |
| Attack confirmed | Server accepts forged token and returns data / elevated access |
| Attack failed | Server rejects forged token move to next attack |
| Claim tamper result | Modified claim accepted or rejected by target endpoint |
Example confirmation:
```bash theme={"system"}
# alg:none attack confirmed
curl https://target.com/api/admin/users \
-H "Authorization: Bearer eyJhbGciOiJub25lIiwidHlwIjoiSldUIn0.\
eyJzdWIiOiIxIiwicm9sZSI6ImFkbWluIn0."
# → 200 OK with admin data
```
#### Known Limitations
* `jwt_tool` and `hashcat` must be installed separately see `references/tools.md`
* `jku`/`x5u` attacks require a publicly reachable server to host the JWKS
* Algorithm confusion attacks require the public key to be accessible (JWKS endpoint or certificate)
* This skill is for authorized testing only always confirm scope before use
***
## Benchmark Results
Tested on claude-sonnet-4-6 via Claude Code CLI. Same prompt, same model, same target. The only variable is whether the skill is loaded.
| Metric | Without Skill | With Skill |
| ----------------- | ------------- | ---------- |
| Turns to complete | 3 | 1 |
| Total tokens | \~14,458 | \~4,866 |
| Time | 355s | 87s |
***
## Related skills
Systematic IDOR/BOLA detection methodology with recon, testing, and bypass techniques
Convert raw pentest notes into structured audit findings ready for reporting
Score a vulnerability using likelihood × impact with SLA-bound remediation urgency