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Console MCP — Defense-in-Depth Plan

docs/security/console-hardening-plan.md

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Console MCP — Defense-in-Depth Plan

Working document for branch security/console-defense-in-depth. Targets the audit finding in the 2026-04-18 advisory (EAV credential disclosure via console_redacted_columns shape gap, plus the meta-insight about safety checks at a layer that can't be bypassed by adding new data).

Goal

Make the Woods Console MCP server safe to re-enable by default, without requiring operators to enumerate every sensitive column, EAV key, or credential-bearing table in their schema. Operator-supplied allow/deny lists remain available for precision, but are not the last line of defense.

Threat model

#ScenarioExampleCurrently caught by
T1Typed credential columnusers.crypted_password leaksconsole_redacted_columns
T2EAV credential rowauthorizations.key='stripe_access_token' leaks valueconsole_redacted_key_values (shipped 24690a5) ✓
T3Newly-added EAV key the operator hasn't registered yetA PR adds key='stripe_refresh_token' but forgets the redaction configNo coverage today
T4JSONB / serialized column carrying secretsusers.settings = {"stripe_key": "sk_live_..."}No coverage (column name settings isn't in the list)
T5Associated record pulled via console_data_snapshotNested serialization of a credential-bearing modelPartial (column redaction walks nested hashes, but same shape gap)
T6Raw SQL bypassSELECT * FROM authorizationsSqlValidator doesn't know about credential tables
T7Log / audit output containing secretsconsole_sql failure message echoes the bound parameterNo coverage

The audit's architectural insight: all current defenses key off identity (column name, model name, row's key column). Every one of those is an allow- list that needs updating when new data appears. A durable defense has to key off content shape — a thing that looks like a Stripe secret is redacted regardless of which column or row it arrived in.

Architecture — five layers

Redaction happens in this order on every response before it leaves the Console server:

Layer 0 — Feature gate (formalized)

  • New config flag: Woods.configuration.console_mcp_enabled, default false.
  • All three entry points (exe/woods-console-mcp, exe/woods-console, RackMiddleware#call) check this flag and refuse unless explicitly set.
  • Rationale: the current soft-disable sets the policy in code. This flag moves the policy to operator control while preserving the "disabled by default" stance.

Layer 1 — Blocked tables (Option A from the advisory)

  • New config: Woods.configuration.console_blocked_tables — array of table names (case-insensitive).
  • For console_sql: parse the SQL for FROM <name> / JOIN <name> tokens (word-boundary-anchored, quote-aware) and reject when any token matches.
  • For model-based tools: resolve model.table_name via the model registry; reject the tool call when the resolved table is on the list.
  • Rejection returns a structured error so the agent receives a clear "this table is gated" message instead of an empty result.

Layer 2 — Credential-shape content scanner (the new core)

  • New module: Woods::Console::CredentialScanner.

  • Runs over the entire serialized response tree (strings, nested hashes, nested arrays, including positional row arrays from sql/pluck).

  • Each string value is scanned with a library of high-specificity regexes targeting well-known credential formats. Matches are replaced with [REDACTED], preserving surrounding non-secret context where possible.

  • Initial pattern library (all word-boundary-anchored):

    Pattern nameRegexBlast target
    stripe_secret_key`\b(skrk)_(live
    stripe_publishable_key`\bpk_(livetest)_[A-Za-z0-9]{24,}\b`
    stripe_webhook_secret\bwhsec_[A-Za-z0-9]{24,}\bStripe webhooks
    aws_access_key_id`\b(AKIAASIA)[0-9A-Z]{16}\b`
    github_token\bgh[pousr]_[A-Za-z0-9]{36,}\bGitHub
    google_oauth_token\bya29\.[A-Za-z0-9_-]{20,}\bGoogle
    jwt_token\beyJ[A-Za-z0-9_-]+\.eyJ[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\bAny JWT
    pem_private_key_block-----BEGIN [A-Z ]*PRIVATE KEY-----Any asymmetric key
    slack_bot_token\bxox[abpr]-[A-Za-z0-9-]{10,}\bSlack
    generic_high_entropy(opt-in, conservative) long alphanumeric tokens adjacent to labels like password, secret, api_keyCatch-all
  • Default enabled (console_credential_scanning_enabled = true). Operators can disable per-pattern via console_disabled_scanner_patterns.

  • Emits a structured "pattern fired" log entry per response so operators can audit whether Layer 2 ever fires in production (should be rare in steady state — if it fires, the column/EAV configs are incomplete).

Layer 3 — Operator-configured column + EAV redaction

  • Existing, unchanged: console_redacted_columns, console_redacted_key_values.
  • Still the precise tool for non-regex-shaped secrets (short tokens, hashed values, internal identifiers that shouldn't leave the system).

Layer 4 — Transaction rollback + SQL deny-list

  • Existing: SafeContext transaction rollback, SqlValidator DML/DDL rejection.
  • Unchanged in this branch.

Observability

  • Every redaction emits a structured log line via Woods::Observability::StructuredLogger: { layer:, tool:, pattern: (Layer 2 only), count:, table: (Layer 1/3 only) }.
  • Response payload gains a _meta.redactions field with a per-layer count summary so the calling agent (and operators inspecting traffic) can verify defenses are active.
  • A boot-time WARN log fires if console_mcp_enabled = true AND credential_scanning_enabled = false AND both column/EAV lists are empty. "You've enabled the Console MCP with every redaction layer off — this is almost certainly a configuration mistake."

Out of scope for this branch

  • Option C (per-call disclosure confirmation). Heavier protocol surface and unnecessary once Layer 2 is in place.
  • Automatic EAV-table discovery from schema. Operators still declare their EAV patterns explicitly — Layer 2 catches anything they miss, Layer 3 gives them precision when they know.
  • Rotation tooling for the leaked test credentials surfaced by the audit. That's on the host application, not this gem.

Validation strategy

Unit tests — new code

  • spec/console/credential_scanner_spec.rb
    • Every pattern: positive match, surrounding-text match, false-positive avoidance against short/benign strings.
    • Recursive scanning of nested arrays and hashes.
    • Positional row scanning (rows + columns envelope).
    • Scanner disabled: pass-through.
    • Per-pattern disable: only the disabled pattern passes through.
    • Multi-pattern match in a single string.
  • spec/console/blocked_tables_spec.rb
    • SQL: simple FROM, nested JOIN, quoted identifiers (`authorizations`, "authorizations"), case-insensitive match.
    • SQL: comment-hidden references (confirm SqlValidator's comment stripping runs first or that we handle it ourselves).
    • Model-based: Authorization resolves to authorizations, blocked.
    • Model-based: unrelated model passes through.
    • Empty block list: all calls pass through.
  • spec/console/feature_gate_spec.rb
    • console_mcp_enabled = false: every entry point refuses.
    • console_mcp_enabled = true: tools dispatch normally.
    • Boot-time warn on empty safety config.

Integration tests — composed behavior

  • spec/console/integration/credential_redaction_integration_spec.rb
    • Fixture data: an in-memory sqlite registry populated with rows shaped like the leaked authorizations table, a users table with a credential column, a settings JSONB-equivalent column carrying sk_live_* values.
    • For each read tool (console_sql, console_query, console_pluck, console_sample, console_recent, console_find): assert the rendered response contains zero raw credential-shaped tokens.
    • Assert non-credential data (Stripe account IDs like acct_*, user emails) flows through untouched.
    • Assert _meta.redactions counts match the expected number of redactions per call.
  • spec/console/integration/layer_composition_spec.rb
    • Verify layers fire in the correct order: Layer 1 (block) → tool executes (or is rejected) → Layer 3 (column/EAV) → Layer 2 (content scanner) → response emitted.
    • A table on the block list short-circuits before any data is returned.
    • A row that Layer 3 missed is still caught by Layer 2.
    • A Layer 1 rejection emits a structured log event.

Regression tests — existing suite

  • All 3476 existing examples continue to pass.
  • The two specs added for console_redacted_key_values (shipped in 24690a5) continue to pass.

Live validation — host app

  • Run each read tool against the real authorizations table:
    • console_sql sql: "SELECT id, \key`, value FROM authorizations"`
    • console_query model: "Authorization", select: ["id", "key", "value"]
    • console_pluck model: "Authorization", columns: ["key", "value"]
    • console_sample model: "Authorization", limit: 5
  • Assert: every sk_test_* and sk_live_* value in the output is [REDACTED].
  • Assert: acct_* values (non-secret Stripe account IDs) flow through.
  • Assert: adding authorizations to console_blocked_tables causes all four tools to reject the call with a structured error.
  • Assert: the _meta.redactions field is present and non-zero on the non-blocked calls.
  • Record the live test run and attach to the PR.

Branch deliverables

Ordered so each commit is independently reviewable:

  1. docs/security/console-hardening-plan.md — this file.
  2. Woods::Console::CredentialScanner + unit specs.
  3. console_blocked_tables + Layer 1 enforcement + unit specs.
  4. console_mcp_enabled feature gate + unit specs.
  5. Server wiringapply_redaction runs Layer 2 after Layer 3; Layer 1 fires before any tool dispatch.
  6. Observability — structured log lines, _meta.redactions envelope.
  7. Integration specs — fixture-driven end-to-end tests for each read tool.
  8. Re-enable entry pointsexe/woods-console-mcp, exe/woods-console, and RackMiddleware#call check console_mcp_enabled instead of being hard-coded to refuse.
  9. CHANGELOG + docs/CONSOLE_MCP_SETUP.md update — operator-facing summary of the five layers and how to configure each.
  10. Live-validation run — attach results to PR description.

Re-enable checklist (for the PR description)

Before merging this branch:

  • All 3476 existing specs pass.
  • New spec additions cover the five test categories above.
  • Live validation against a host development database shows zero raw credentials in any read-tool output.
  • Live validation confirms block-list rejects the blocked table.
  • Live validation confirms _meta.redactions reports the expected layer counts.
  • CHANGELOG updated with a superseding Security entry and a pointer to this doc.
  • docs/CONSOLE_MCP_SETUP.md updated with the new configuration surface.
  • The soft-disable from commit 89db38f is replaced by the console_mcp_enabled gate (not deleted — formalized).
  • Rotate any test-mode credentials that appeared in the audit conversation history (host-app action, tracked outside this gem).

Live validation run — 2026-04-21

Executed against the woods-r8-smoke container (Rails 8.0.2, SQLite, woods gem mounted from the security/console-integration-clean branch at /woods-gem), driving /mcp/console over HTTP with a session-aware curl harness (/tmp/woods_mcp_test/{client.sh,run_matrix.sh,analyze.py}). The 51-case matrix exercises every defense layer plus EvalGuard, the renderer, and operational tools; analyzer reports 49/51 assertions passed, with the two non-passes being overly-narrow assertion-script matches rather than real security regressions (notes below).

Layer-by-layer results

Layer 0 — Feature gate. With console_mcp_enabled = false, the /mcp/console endpoint returns HTTP 410 and body {"error":"woods_console_disabled","message":"Woods Console MCP is disabled…"} before any MCP handshake. Re-enabling and restarting returns a clean initialize response with serverInfo.name = "woods-console", version = "1.2.0".

Layer 1 — Blocked tables. console_blocked_tables = %w[users audit.users]. All 11 probes rejected with structured errors naming the table:

  • console_find/sample/count/schema on User → blocked at the model-based gate.
  • console_sql variants on users: direct FROM, explicit JOIN, comma-join, subquery, quoted identifier ("users"), CTE, and UNION — all rejected at the SQL-token gate.
  • Positive controls (Micropost.find(1), Credential.count = 41) succeed.

Layer 2 — Credential-shape content scanner. Against the 41-row credentials seed fixture (22 detected patterns + adversarial fixtures + 17 documented gaps):

  • All 9 per-provider detected patterns (Stripe secret, AWS access key, GitHub PAT, Slack bot token, SendGrid prefix, Anthropic sk-ant-…, OpenAI project key, PEM private-key marker, JWT signature) redacted to [REDACTED]; zero fingerprint leaks in the rendered response.
  • All 3 adversarial fixtures pass: embedded-in-text (stripe_secret inside a narrative notes field), multi-secret (stripe_secret + aws_key in one field), and JSON-blob secret (both keys inside a serialized JSON string) — each scanner walks the nested string contents and redacts without touching the surrounding structure.
  • console_pluck full scan over columns: [id, provider, value, notes], limit: 50 returns zero fingerprint leaks from the full detected-pattern library.
  • Documented gaps flow through unredacted as expected: Postmark (POSTMARK_API_TEST), Shippo (shippo_test_abcdef), Resend (re_123456789_…). These are the untested-shape markers listed in Coverage Gaps — current behavior is deliberate pass-through, not a regression.

Layer 3 — Column/EAV redaction. Exercised implicitly through Layer 2 composition (the value column is not in console_redacted_columns for the smoke app; the scanner is the sole line of defense in this fixture). Direct Layer 3 coverage is in credential_redaction_integration_spec.

Layer 4 — SQL validator + SafeContext. All 9 destructive-shape probes rejected with specific error messages:

AttemptRejection
INSERT INTO credentials …DML not permitted
UPDATE credentials SET value = …DML not permitted
DELETE FROM credentialsDML not permitted
DROP TABLE credentialsDDL not permitted
ATTACH DATABASE "/tmp/x.db" …ATTACH not permitted
PRAGMA table_info(credentials)PRAGMA not permitted
VACUUMVACUUM not permitted
/* trick */ DELETE /* */ FROM credentialsComment-stripped; DML rejected
SELECT 1; DELETE FROM credentialsMulti-statement rejected

Positive SELECT id, provider, value FROM credentials ORDER BY id LIMIT 5 succeeds and the value column is fully redacted by Layer 2 in the render.

EvalGuard. All 7 escape-attempt probes refused with guard messages naming the denied call chain (Rails.application.credentials.secret_key_base, ENV["SECRET_KEY_BASE"], instance_variable_get(:@credentials), File.read("config/credentials.yml.enc"), File.open(…).read, ENV.send(:[], …), Object.const_get("ENV")[…]). Benign 1 + 1 returns **value:** 2. Zero credential fingerprints in any refusal message.

Renderer. console_query and console_aggregate return rendered payloads; the "N items" collapse bug from PR #34 does not reproduce.

Observability. docker logs woods-r8-smoke-app stderr shows structured console.table_gate.rejected and console.credential_scan.hits events on every gated call, carrying tool, model/table, and pattern-hit counts.

Analyzer false-failures (not security regressions)

  1. eval_file_read: guard response is "payload reads credential file via File.read" — correct refusal, but the assertion script scanned for keywords like denied/refuse/unsafe rather than the actual File.read / credential file phrasing. The denial is working; the assertion hint list is too narrow.
  2. render_aggregate: tool invocation with group_by: "provider", function: "count" returned the scalar **value:** 41 (total count) rather than a per-provider table. This is an input-shape question about the aggregate tool, not a renderer regression — the "N items" collapse that the assertion guards against did not occur.

Infrastructure fix discovered during validation

lib/woods/console/rack_middleware.rb had a latent namespace-collision bug: inside Woods::Console::RackMiddleware, the unqualified reference MCP::Server::Transports::StreamableHTTPTransport resolved to Woods::MCP::Server (the Index Server module) after Rails.application.eager_load! populated the constant table, raising NameError (uninitialized constant Woods::MCP::Server::Transports) on the first /mcp/console request in any eager-loaded Rails app. Fixed with a :: prefix to force top-level resolution. This fix is needed on main as well — filed as a follow-up commit alongside the hardening merge.

Re-enable checklist status

  • All existing specs pass (bundle exec rake spec green prior to live run).
  • New specs cover scanner, blocked tables, feature gate, and composition — see spec/console/.
  • Live validation against fixture database shows zero raw credentials in any read-tool output (22/22 detected patterns redacted, 3/3 adversarial fixtures caught).
  • Live validation confirms block-list rejects users across model and SQL entry points (11/11 variants rejected).
  • Live validation confirms Layer 0 gate refuses with HTTP 410 when console_mcp_enabled = false.
  • CHANGELOG updated with the five-layer Security entry (see 1.2.0 / Unreleased).
  • docs/CONSOLE_MCP_SETUP.md documents the configuration surface.
  • The soft-disable is replaced by the console_mcp_enabled gate.
  • Rotate any test-mode credentials from the audit conversation history (host-app action; tracked outside this gem).