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Vault MCP
Model Context Protocol (MCP) Server for HashiCorp Vault secret management
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Vault MCP
MCP server for credential isolation in LLM agents. Your bot uses passwords and API keys — but never sees them in its context window.
The Problem
User LLM Website
│ │ │
│ "password: MyP@ss!" │ │
├───────────────────────►│ │
│ │──── MyP@ss! ──────────►│
│ │ │
│ │◄──── 200 OK ───────────│
│ │ │
▼ ▼ ▼
┌──────────────┐
│ MyP@ss! is │
│ now stored │
│ in LLM │
│ context, │
│ conversation │
│ history, │
│ session logs │
└──────────────┘
The Solution
User Browser Form Vault MCP LLM Website
│ (localhost) │ │ │
│ ●●●●●●●● │ │ │ │
├──────────────►│ │ │ │
│ │── encrypt ─────►│ │ │
│ │ │◄── vault_login ─┤ │
│ │ │── fill form ───────────────────►│
│ │ │◄──── 200 OK ───────────────────┤
│ │ │── { status: ok }─►│ │
│ │ │ │ │
▼ ▼ ▼ ▼ ▼
┌──────────────┐ ┌──────────────┐
│ Password: │ │ LLM context: │
│ AES-256-GCM │ │ │
│ encrypted │ │ "status: ok" │
│ on disk │ │ (no password)│
└──────────────┘ └──────────────┘
Scenarios
Scenario 1: First-time Login (vault_add → vault_login)
The agent needs credentials it doesn't have. It calls vault_add() — a browser form opens where you enter the password. Then vault_login() fills the form via Chrome.
User Claude Code Vault MCP Chrome
│ │ │ │
│ "Log me into │ │ │
│ Jira" │ │ │
├───────────────────►│ │ │
│ │── vault_list() ────►│ │
│ │◄─ { credentials:[] }┤ │
│ │ │ │
│ │── vault_add ───────►│ │
│ │ { site: "jira" } │ │
│ │ │ │
│ ┌────────────────────────────┐ │ │
│ │ Browser opens │ │ │
│ │ localhost:9900/add │ │ │
│ │ │ │ │
│ │ Site ID: [jira] │ │ │
│ │ Email: [me@work.com] │ │ │
│ │ Password: [●●●●●●●●●●] │ │ │
│ │ URL: [jira.com/login]│ │ │
│ │ │ │ │
│ │ [Add to Vault] │ │ │
│ └────────────┬───────────────┘ │ │
│ │ │ │
│ └── POST (encrypted) ────►│ │
│ │ │
│ │◄─ { status: ok } ───┤ │
│ │ site_id: "jira" │ │
│ │ │ │
│ │ (no password │ │
│ │ in this response) │ │
│ │ │ │
│ │── vault_login ─────►│ │
│ │ { site: "jira" } │── decrypt ──┐ │
│ │ │◄────────────┘ │
│ │ │── fill email ────►│
│ │ │── fill pass ────►│
│ │ │── click submit ──►│
│ │ │◄─ page loaded ───┤
│ │ │── clear pass ────►│
│ │ │ │
│ │◄─ { status: ok, ───┤ │
│ │ title: "Jira │ │
│ │ Dashboard" } │ │
│ │ │ │
│◄── "You're logged │ │ │
│ into Jira!" │ │ │
Scenario 2: API Key Proxy (vault_api_request)
The agent makes an API call. Vault injects the API key into headers — the key never appears in the LLM context.
Claude Code Vault MCP Stripe API
│ │ │
│── vault_api_request ►│ │
│ service: "stripe" │ │
│ url: "/v1/charges" │ │
│ method: "GET" │ │
│ │── decrypt API key │
│ │ │
│ │── GET /v1/charges ────────►│
│ │ Authorization: │
│ │ Bearer sk-live-**** │
│ │ │
│ │◄── { data: [...] } ───────┤
│ │ │
│ │── scan response │
│ │ for leaked key │
│ │ (replace with ***) │
│ │ │
│◄── { status: ok, ───┤ │
│ body: "..." } │ │
│ │ │
│ (API key NOT in │ │
│ this response) │ │
Scenario 3: Returning User (credentials already stored)
If credentials already exist, the agent skips vault_add and goes straight to vault_login:
User Claude Code Vault MCP Chrome
│ │ │ │
│ "Open GitHub" │ │ │
├───────────────────►│ │ │
│ │── vault_list() ────►│ │
│ │◄─ [{ siteId: ─┤ │
│ │ "github", │ │
│ │ active: true }] │ │
│ │ │ │
│ │── vault_login ─────►│ │
│ │ { site: "github" }│── decrypt ───┐ │
│ │ │◄─────────────┘ │
│ │ │── CDP login ─────►│
│ │ │◄─ success ───────┤
│ │◄─ { status: ok } ───┤ │
│ │ │ │
│◄── "Done!" │ │ │
Scenario 4: Credential Revocation
Remove access instantly — the agent can no longer use the credential:
Admin (CLI) Vault MCP Claude Code
│ │ │
│── vault-mcp remove │ │
│ "jira" │ │
│ │── delete from store │
│ │── audit: removed │
│◄── "Removed: jira" │ │
│ │ │
│ │ ... later ... │
│ │ │
│ │◄── vault_login ──────┤
│ │ { site: "jira" } │
│ │ │
│ │── { status: FAIL, ──►│
│ │ "Credential not │
│ │ found: jira" } │
│ │ │
Scenario 5: Audit Trail
Every credential use is logged with a tamper-proof hash chain:
~/.vault-mcp/audit.jsonl
┌─────────────────────────────────────────────────────────────┐
│ evt_001 │ credential.created │ jira │ success │ hash_1 │
│ │ │ │ │ │ │
│ evt_002 │ credential.used │ jira │ success │ │ │
│ │ bot: claude │ │ │ ▼ │
│ │ │ │ prevHash: hash_1 │
│ │ │ │ │ hash_2 │
│ │ │ │ │ │ │
│ evt_003 │ credential.used │ jira │ success │ ▼ │
│ │ bot: claude │ │ prevHash: hash_2 │
│ │ │ │ │ hash_3 │
│ │ │ │ │ │ │
│ evt_004 │ credential.removed │ jira │ success │ ▼ │
│ │ │ │ prevHash: hash_3 │
└─────────────────────────────────────────────────────────────┘
Modify any entry → hash chain breaks → tamper detected
$ vault-mcp audit
Chain integrity: VALID (4 entries)
Quickstart
# 1. Clone and build
git clone https://github.com/Chill-AI-Space/vault-mcp.git
cd vault-mcp
npm install
npm run build
# 2. Register with Claude Code
claude mcp add -s user vault -- node ~/path/to/vault-mcp/dist/index.js
# 3. Use in Claude Code
# "Log me into GitHub" →
# Claude calls vault_add("github") → browser form opens → you enter password
# Claude calls vault_login("github") → Chrome logs in via CDP
# Claude sees only { status: "success" }
Or add credentials via CLI (outside of Claude Code):
vault-mcp add --site github --email you@example.com --url https://github.com/login
# Password is prompted interactively (masked with *)
MCP Tools
| Tool | What it does | What the LLM sees |
|---|---|---|
vault_add(site_id?) | Opens browser form for secure credential entry | { status, site_id } |
vault_login(site_id) | Logs into website via Chrome CDP | { status, page_title } |
vault_api_request(service, url, ...) | Makes API call with injected credentials | { status, body } |
vault_list() | Lists stored credentials | [{ siteId, type, active }] |
vault_status(site_id) | Shows credential metadata + audit stats | { siteId, active, lastUsed } |
What the LLM never sees: passwords, API keys, emails, tokens, encrypted data.
CLI Commands
vault-mcp add # Interactive: add credential (password masked)
vault-mcp add --site X --email Y # Semi-interactive
vault-mcp list # List credentials (no secrets)
vault-mcp remove <site_id> # Remove credential
vault-mcp audit [site_id] # View audit log + chain integrity
vault-mcp dashboard # Web UI on localhost:9900
vault-mcp serve # Start MCP server (for debugging)
Architecture
vault-mcp/
├── src/
│ ├── index.ts ── Entry: CLI or MCP mode (auto-detect)
│ ├── server.ts ── MCP server, 5 tools registered
│ ├── cli.ts ── CLI commands (commander + inquirer)
│ ├── tools/
│ │ ├── vault-add.ts ── Opens browser form, waits for submit
│ │ ├── vault-login.ts ── Decrypt → CDP → fill form → status
│ │ ├── vault-api.ts ── Decrypt → inject headers → fetch → sanitize
│ │ ├── vault-list.ts ── Return metadata only
│ │ └── vault-status.ts ── Metadata + audit stats
│ ├── store/
│ │ ├── encrypted-store.ts ── AES-256-GCM CRUD, JSON file backend
│ │ └── keychain.ts ── Master key: env var or auto-generate
│ ├── browser/
│ │ └── cdp-bridge.ts ── Playwright connectOverCDP, form fill
│ ├── audit/
│ │ └── logger.ts ── Append-only JSONL, SHA-256 hash chain
│ └── dashboard/
│ ├── server.ts ── HTTP server (127.0.0.1:9900 only)
│ ├── index.html ── Full dashboard (CRUD + audit viewer)
│ └── add.html ── Focused add-credential form (for vault_add)
└── test/ ── 29 tests including credential sanitization
Configuration
| Env Variable | Default | Description |
|---|---|---|
VAULT_MASTER_KEY | (auto-generated) | Encryption key. Without it, a random key is saved to ~/.vault-mcp/.master-key |
VAULT_CDP_URL | http://localhost:9222 | Chrome DevTools Protocol endpoint |
# Register with env vars
claude mcp add -s user vault \
-e VAULT_MASTER_KEY=my-secret-key \
-e VAULT_CDP_URL=ws://localhost:9222 \
-- node ~/path/to/vault-mcp/dist/index.js
Storage
~/.vault-mcp/
├── credentials.json ── Encrypted credentials (AES-256-GCM, unique IV per entry)
├── audit.jsonl ── Append-only log with SHA-256 hash chain
└── .master-key ── Auto-generated master key (mode 0600)
Security
See SECURITY.md for full threat model.
Protects against Does NOT protect against
───────────────── ────────────────────────
✓ LLM context leakage ✗ User typing password in chat
✓ Plaintext credential storage ✗ Compromised host (root access)
✓ Audit log tampering ✗ Malicious MCP client
✓ Accidental exposure in logs ✗ Browser-level memory attacks
Testing
npm test # 29 tests
npm run test:watch # Watch mode
Tests verify: encryption round-trip, wrong-key rejection, credential sanitization in all tool responses, hash chain integrity, tamper detection, full lifecycle flows.
License
MIT