CVE-2026-49257: mcp-pinot: Unauthenticated tool invocation via default oauth_enabled=False + host 0.0.0.0 bind

Resolution

Fixed in v3.1.0, released 2026-05-25. The fix was merged in PR #95 at commit 1c7d3f9.

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 oauthenabled=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: mcppinot/server.py, mcppinot/config.py.

Root cause

Three defaults compose to produce unauthenticated network exposure:

1. Auth is opt-in and defaults to off (mcppinot/config.py:64,328):

python @dataclass class ServerConfig: ... oauthenabled: bool = False ...

def loadserverconfig() -> ServerConfig: return ServerConfig( ... oauthenabled=os.getenv("OAUTHENABLED", "false").lower() == "true", ... )

2. Auth construction is gated by oauthenabled (mcppinot/server.py:26-46):

python auth = None if serverconfig.oauthenabled: oauthconfig = loadoauthconfig() tokenverifier = JWTVerifier(...) auth = OAuthProxy(...)

mcp = FastMCP("Pinot MCP Server", auth=auth)

When oauthenabled 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 (mcppinot/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 (mcppinot/config.py:285-294, 300-315). When an unauthenticated MCP caller invokes readquery or any other tool, the request is executed with the server's PINOTTOKEN or PINOTUSERNAME/PINOTPASSWORD, 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 mcppinot/server.py are exposed without auth in the default configuration:

| Tool | Impact when unauthenticated | |---|---| | readquery | Arbitrary SELECT against any table allowed by server-side filter (or all tables if no filter) | | listtables | Enumerate cluster schemas | | tabledetails, segmentlist, segmentmetadatadetails, tableconfigschemadetails, indexcolumndetails, getschema, gettableconfig | Read cluster metadata | | createschema, updateschema | Create or mutate Pinot schemas | | createtableconfig, updatetableconfig | Create or mutate table configurations | | reloadtablefilters | Reload server filter file; response leaks previousfilters and newfilters lists | | testconnection | 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":"listtables","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":"readquery", "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":"createschema", "arguments":{ "schemaJson":"{\"schemaName\":\"attackerschema\",\"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 createschema, updateschema, createtableconfig, updatetableconfig | | 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 MCPHOST, 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" - serverconfig.oauthenabled is False - serverconfig.host is not a loopback address (e.g. not in {"127.0.0.1", "::1", "localhost"})

Sample:

python def isloopback(host: str) -> bool: return host in {"127.0.0.1", "::1", "localhost"}

def main(): ... if serverconfig.transport != "stdio" and not serverconfig.oauthenabled and not isloopback(serverconfig.host): raise SystemExit( "Refusing to start: HTTP transport bound to non-loopback host " f"({serverconfig.host}) without OAuth. Set OAUTHENABLED=true or " "set MCPHOST=127.0.0.1 for local-only access." ) ...

B. Default oauthenabled 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 MCPHOST=127.0.0.1 for stdio/local-only deployments

Resources

- mcppinot/server.py lines 26-46, 248-269 - mcppinot/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.