CVE-2026-49257 — Vulnerability in mcp-pinot-server — CVE Details

## Resolution Fixed in [v3.1.0](https://github.com/startreedata/mcp-pinot/releases/tag/v3.1.0), released 2026-05-25. The fix was merged in [PR #95](https://github.com/startreedata/mcp-pinot/pull/95) at commit [`1c7d3f9`](https://github.com/startreedata/mcp-pinot/commit/1c7d3f9cd384854bf72c127d230bdb32299475ad). The fix changes the default HTTP bind host to `127.0.0.1`, refuses non-loopback HTTP/HTTPS exposure unless OAuth is enabled, makes Helm exposure opt-in and OAuth-gated, and adds parser-backed single-statement read-only validation for `read-query`. ## CVSS evaluation Reviewed on 2026-05-25. The advisory remains **Critical** with `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H` = **10.0**. Rationale: | Metric | Value | Reason | |---|---|---| | AV | Network | The default HTTP server bound to `0.0.0.0:8080` and accepted remote HTTP requests. | | AC | Low | Exploitation required only a direct MCP tool call. | | PR | None | OAuth was disabled by default. | | UI | None | No user interaction was required. | | S | Changed | The vulnerable MCP server used its server-side credentials to act on the separate Pinot cluster security boundary. | | C | High | Unauthenticated callers could read table data and cluster metadata through server-side Pinot credentials. | | I | High | Unauthenticated callers could create or update schemas and table configs where the server-side account had those privileges. | | A | High | Expensive queries and configuration mutations could degrade or disrupt Pinot availability. | # Unauthenticated tool invocation via default oauth_enabled=False + host 0.0.0.0 bind ## Summary `mcp-pinot` v3.0.1 (and earlier) defaults to running an HTTP MCP server bound to `0.0.0.0:8080` with no authentication enabled. All MCP tools, including SQL query execution, schema creation, and table-config mutation, are reachable by any network-adjacent caller. The server proxies these calls using server-side Pinot credentials, producing a confused-deputy condition that yields full read/write access to the configured Pinot cluster. ## Affected versions - All releases on `main`, confirmed in tags v2.1.0 through v3.0.1. - Affected files: `mcp_pinot/server.py`, `mcp_pinot/config.py`. ## Root cause Three defaults compose to produce unauthenticated network exposure: **1. Auth is opt-in and defaults to off** (`mcp_pinot/config.py:64,328`): ```python @dataclass class ServerConfig: ... oauth_enabled: bool = False ... def load_server_config() -> ServerConfig: return ServerConfig( ... oauth_enabled=os.getenv("OAUTH_ENABLED", "false").lower() == "true", ... ) ``` **2. Auth construction is gated by `oauth_enabled`** (`mcp_pinot/server.py:26-46`): ```python _auth = None if server_config.oauth_enabled: oauth_config = load_oauth_config() token_verifier = JWTVerifier(...) _auth = OAuthProxy(...) mcp = FastMCP("Pinot MCP Server", auth=_auth) ``` When `oauth_enabled` is false (default), `_auth` stays `None` and `FastMCP` registers all `@mcp.tool` endpoints with no authentication. **3. Default bind is all interfaces on a well-known port** (`mcp_pinot/config.py:60-61`): ```python host: str = "0.0.0.0" port: int = 8080 ``` The HTTP transport in `server.py:263-268` uses these values directly. Any operator following the README's HTTP transport instructions (`uv pip install`, `.env` from `.env.example`, run) ends up with a network-reachable MCP server with no auth. ## Confused-deputy The Pinot client uses server-side credentials loaded from environment variables (`mcp_pinot/config.py:285-294, 300-315`). When an unauthenticated MCP caller invokes `read_query` or any other tool, the request is executed with the server's `PINOT_TOKEN` or `PINOT_USERNAME`/`PINOT_PASSWORD`, which is typically a privileged service account. The MCP server effectively launders the caller's lack of identity into the server's privileges against the upstream cluster. ## Exposed tools All 14 tools in `mcp_pinot/server.py` are exposed without auth in the default configuration: | Tool | Impact when unauthenticated | |---|---| | `read_query` | Arbitrary SELECT against any table allowed by server-side filter (or all tables if no filter) | | `list_tables` | Enumerate cluster schemas | | `table_details`, `segment_list`, `segment_metadata_details`, `tableconfig_schema_details`, `index_column_details`, `get_schema`, `get_table_config` | Read cluster metadata | | `create_schema`, `update_schema` | Create or mutate Pinot schemas | | `create_table_config`, `update_table_config` | Create or mutate table configurations | | `reload_table_filters` | Reload server filter file; response leaks `previous_filters` and `new_filters` lists | | `test_connection` | Cluster diagnostics including host, port, scheme, database, and auth-mode | ## Reproduction Minimal reproduction against a default-configured `mcp-pinot` v3.0.1 instance running on `http://victim:8080/mcp`: ```bash # 1. Enumerate tables (no Authorization header) curl -X POST http://victim:8080/mcp \ -H 'Content-Type: application/json' \ -d '{ "jsonrpc":"2.0", "method":"tools/call", "params":{"name":"list_tables","arguments":{}}, "id":1 }' # 2. Read arbitrary table contents (server forwards using its own Pinot credentials) curl -X POST http://victim:8080/mcp \ -H 'Content-Type: application/json' \ -d '{ "jsonrpc":"2.0", "method":"tools/call", "params":{ "name":"read_query", "arguments":{"query":"SELECT * FROM <table> LIMIT 100"} }, "id":2 }' # 3. Create a new schema (write privileges) curl -X POST http://victim:8080/mcp \ -H 'Content-Type: application/json' \ -d '{ "jsonrpc":"2.0", "method":"tools/call", "params":{ "name":"create_schema", "arguments":{ "schemaJson":"{\"schemaName\":\"attacker_schema\",\"dimensionFieldSpecs\":[{\"name\":\"id\",\"dataType\":\"STRING\"}]}" } }, "id":3 }' ``` ## Severity (CVSS 3.1) `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H` = **10.0 Critical** | Metric | Value | Reason | |---|---|---| | AV (Attack Vector) | Network | Server defaults to bind on `0.0.0.0:8080` | | AC (Attack Complexity) | Low | No special conditions, single HTTP request | | PR (Privileges Required) | None | No authentication required in default config | | UI (User Interaction) | None | Direct unauthenticated call | | S (Scope) | Changed | Vulnerable MCP component grants access to a separate Pinot cluster (different security authority) | | C (Confidentiality) | High | Full read of any table data the server-side account can reach | | I (Integrity) | High | Schema and table-config writes via `create_schema`, `update_schema`, `create_table_config`, `update_table_config` | | A (Availability) | High | Heavy queries, malformed configs, or schema overrides can degrade or break the cluster | If the operator restricts the bind address to `127.0.0.1` via `MCP_HOST`, AV drops to `Local` and the score reduces. But this is not the documented default. ## Suggested remediation Two independent hardenings, both recommended: **A. Refuse to start in an insecure default**, in `server.py` `main()`, fail-closed when: - `transport != "stdio"` - `server_config.oauth_enabled` is `False` - `server_config.host` is not a loopback address (e.g. not in `{"127.0.0.1", "::1", "localhost"}`) Sample: ```python def _is_loopback(host: str) -> bool: return host in {"127.0.0.1", "::1", "localhost"} def main(): ... if server_config.transport != "stdio" and not server_config.oauth_enabled and not _is_loopback(server_config.host): raise SystemExit( "Refusing to start: HTTP transport bound to non-loopback host " f"({server_config.host}) without OAuth. Set OAUTH_ENABLED=true or " "set MCP_HOST=127.0.0.1 for local-only access." ) ... ``` **B. Default `oauth_enabled` to `True`** and require explicit opt-out for local development. This matches the principle of secure-by-default for network-facing services. **C. Document the threat model** in README under a "Production deployment" section, including: - Explicit warning that the server should not be exposed to untrusted networks without OAuth - Recommendation to set `MCP_HOST=127.0.0.1` for stdio/local-only deployments ## Resources - `mcp_pinot/server.py` lines 26-46, 248-269 - `mcp_pinot/config.py` lines 56-65, 318-330 - FastMCP `auth` parameter behavior when `None`: https://github.com/jlowin/fastmcp - The Register, May 13 2026: MCP database flaws across Doris, Pinot, RDS ## Reporter Independent security researcher. Disclosed via GitHub Security Advisory, 2026-05-23.