NotebookLM MCP is an MCP server and HTTP service for interacting with Google NotebookLM and exporting generated content to local vault directories. Versions 1.6.0 through 2.0.2 contain a path traversal vulnerability in the `POST /batch-to-vault` endpoint, also exposed through the `batch_to_vault` MCP tool beginning in version 1.7.0, because attacker-controlled `vault_dir` and `slug_prefix` values can cause Markdown and JSON files to be written outside the intended vault directory to any location writable by the server process. Version 2.0.3 sanitizes `slug_prefix` and supports vault containment when `NOTEBOOKLM_VAULT_ROOT` is configured; containment is not enabled if that variable is unset. Users unable to upgrade should run the server as a dedicated unprivileged account restricted to the intended vault, keep the HTTP endpoint limited to localhost, and validate `vault_dir` values supplied by LLMs processing untrusted content.

Affected: npm: @roomi-fields/notebooklm-mcp

## Summary

The `vault_batch` MCP tool (and the equivalent `POST /batch-to-vault` HTTP endpoint) accepted a caller-supplied `vault_dir` path that was passed directly to `path.resolve()` + `fs.mkdir()` with no containment check. A caller — or a prompt-injected LLM driving the MCP — could therefore create directories and write `.md` / `.json` answer files anywhere the server process can write.

The `slug_prefix` parameter had a parallel, smaller traversal vector: it was concatenated into the filename without sanitization, so a prefix containing `/` or `..` could escape the resolved vault directory through the filename component.

## Impact

File write (markdown + JSON sidecars) to any location writable by the server process. The written files are inert content (no code execution by themselves), but in a multi-user context — or when the MCP server is driven by an LLM that has read untrusted content (prompt injection) — this allows an attacker to plant files in sensitive locations (autostart folders, shell startup files, etc.) for downstream exploitation.

The vulnerability exists from **v1.6.0** (when the HTTP `/batch-to-vault` endpoint was introduced) and v1.7.0 (when the same logic was exposed as the `batch_to_vault` MCP tool) through **v2.0.2**.

## Patch

Fixed in **v2.0.3**:

- **Opt-in containment via `NOTEBOOKLM_VAULT_ROOT` env var.** When set, `vault_dir` is resolved relative to that root and `realpath`-based containment is enforced. Absolute paths or `..` segments outs…