Individual skill
hunt-grpc
Hunt gRPC vulnerabilities — server reflection enabled (enumerate all services/methods), missing authentication / metadata-stripping on internal endpoints, plaintext gRPC over HTTP/2, internal endpoint disclosure, proto file leakage, gRPC-Web/grpc-gateway transcoding injection, and HTTP/2 Rapid Reset DoS (CVE-2023-44487). Use when target exposes port 50051 / 443 / 8443 / 9090 with HTTP/2, when grpcurl/grpcui detects reflection, when an Envoy or grpc-gateway proxy is fronting a microservice, or when recon reveals a microservice architecture.
skills/hunt-grpc/SKILL.md
Source commit 961a0dd3d2d2f66a07a416ade3b1d4473b64802e
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- Last checked
- Nov 4, 2026
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- Repository last updated
- Nov 5, 2026
- License
- Apache-2.0
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# 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.**
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