SpiceDB binding metrics port to untrusted networks and can leak command-line flags

Summary

SpiceDB is an open source, Google Zanzibar-inspired, database system for creating and managing security-critical application permissions. The `spicedb serve` command contains a flag named `--grpc-preshared-key` which is used to protect the gRPC API from being accessed by unauthorized requests. The values of this flag are to be considered sensitive, secret data. The `/debug/pprof/cmdline` endpoint served by the metrics service (defaulting running on port `9090`) reveals the command-line flags provided for debugging purposes. If a password is set via the `--grpc-preshared-key` then the key is revealed by this endpoint along with any other flags provided to the SpiceDB binary. This issue has been fixed in version 1.19.1.

### Impact

All deployments abiding by the recommended best practices for production usage are **NOT affected**: - Authzed's SpiceDB Serverless - Authzed's SpiceDB Dedicated - SpiceDB Operator

Users configuring SpiceDB via environment variables are **NOT affected**.

Users **MAY be affected** if they expose their metrics port to an untrusted network and are configuring `--grpc-preshared-key` via command-line flag.

### Patches

TODO

### Workarounds

To workaround this issue you can do one of the following:

- Configure the preshared key via an environment variable (e.g. `SPICEDB_GRPC_PRESHARED_KEY=yoursecret spicedb serve`) - Reconfigure the `--metrics-addr` flag to bind to a trusted network (e.g. `--metrics-addr=localhost:9090`) - Disable the metrics service via the flag (e.g. `--metrics-enabled=false`) - Adopt one of the recommended deployment models: [Authzed's managed services](https://authzed.com/pricing) or the [SpiceDB Operator](https://github.com/authzed/spicedb-operator)

### References

- [GitHub Security Advisory issued for SpiceDB](https://github.com/authzed/spicedb/security/advisories/GHSA-cjr9-mr35-7xh6) - [Go issue #22085](https://github.com/golang/go/issues/22085) for documenting the risks of exposing pprof to the internet - [Go issue #42834](https://github.com/golang/go/issues/42834) discusses preventing pprof registration to the default serve mux - [semgrep rule go.lang.security.audit.net.pprof.pprof-debug-exposure](https://semgrep.dev/r?q=go.lang.security.audit.net.pprof) checks for a variation of this issue

### Credit

We'd like to thank Amit Laish, a security researcher at GE Vernova for responsibly disclosing this vulnerability.