Kozou: Unauthenticated MCP HTTP server and bundled dev-stack hardening (DNS-rebinding, request-body limits, read-only reads, default network exposure)

Overview

Kozou compiles a PostgreSQL schema into an Admin UI, a REST API, and an MCP server. Several hardening gaps in the bundled HTTP surfaces and the scaffolded dev stack are fixed in 1.8.1.

Issues

1. MCP HTTP server lacked DNS-rebinding protection. The Streamable HTTP transport is unauthenticated and loopback by default. Without Host/Origin validation, a malicious web page in the operator's browser could rebind a hostname it controls to the loopback address and drive the MCP endpoint — reading schema metadata, or (when the opt-in call execution tool is enabled) executing exposed functions as the execution role.

2. Unbounded request-body buffering (DoS). Both the MCP HTTP server and the in-house REST server read the entire request body into memory with no size limit, so a reachable client could drive the process toward memory exhaustion.

3. Read requests ran in a read/write transaction. The shared role-transaction envelope opened every request with a plain BEGIN, so a GET ran read/write. A SELECT that reaches a volatile function or a writable / INSTEAD-triggered view could perform a write that then commits — the "a GET only reads" contract was left to the serving role's grants rather than enforced.

4. No-auth dev surfaces published on all interfaces by default. The scaffolded docker-compose.yml (and the quickstart) published the unauthenticated Admin UI and MCP HTTP server — and the default-credential demo database — on every host interface, and the config defaulted those binds to 0.0.0.0.

What changed in 1.8.1

• DNS-rebinding guard (MCP HTTP): the server validates the Host header (and a present Origin) against an allowlist before handling any request, on every route. Matching is on the hostname; loopback names are always accepted and an operator can add hosts via configuration. A browser cannot forge Host/Origin, so this closes the rebinding vector. (This is a browser-rebinding defence; network reachability of an unauthenticated server must still be constrained by the network — see workarounds.)
• Request-body size cap: both HTTP servers reject an over-large declared Content-Length (413) and enforce the limit while streaming, so a chunked / Content-Length-less body cannot grow unbounded. A non-JSON Content-Type on a body is rejected with 415. The cap is configurable.
• Read-only read transactions: read methods (GET) now run in a READ ONLY transaction, so the database refuses any write for the duration of the request regardless of the role's grants.
• Loopback-by-default network posture: the Admin UI and MCP HTTP server now bind loopback by default; the bundled compose files publish every host port (Admin UI, MCP, database) on 127.0.0.1 only, while the container binds all interfaces internally so the loopback mapping still works. Operators opt into a broader bind explicitly.

Impact

The MCP HTTP server's exposure is greatest when the opt-in call execution tool is enabled and/or the server is reachable beyond loopback. The read/write-transaction issue has effect only when the schema exposes a read path that can write (a volatile-function-backed column or a writable/INSTEAD-triggered view) and the serving role holds write grants. The all-interface publish affected anyone who ran the scaffolded docker compose up on a host reachable from an untrusted network. Requests run under SET LOCAL ROLE, so PostgreSQL still enforces grants/RLS at runtime; these are defense-in-depth and read-contract hardening.

Affected / patched

• npm packages kozou, @kozou/api, @kozou/mcp, @kozou/core (and the lockstep-versioned siblings): affected <= 1.8.0, patched 1.8.1.
• Container image ghcr.io/kozou-dev/kozou: patched at tag v1.8.1.

Workarounds (if you cannot upgrade immediately)

• Bind the Admin UI and MCP HTTP server to loopback and publish their host ports on 127.0.0.1 only; do not expose them to untrusted networks.
• Do not enable the MCP call execution tool on a non-loopback / unauthenticated deployment.
• Put an authenticating reverse proxy (with Host/Origin validation and a request-body limit) in front of any non-loopback deployment.
• Change the demo database's default credentials and restrict its port.

Patches

Upgrade to Kozou 1.8.1 (all npm packages and the ghcr.io/kozou-dev/kozou image).

Affected packages

• kozou <= 1.8.0
• @kozou/api <= 1.8.0
• @kozou/mcp <= 1.8.0
• @kozou/core <= 1.8.0

Remediation

Upgrade to a patched release:

• kozou 1.8.1
• @kozou/api 1.8.1
• @kozou/mcp 1.8.1
• @kozou/core 1.8.1