Path traversal vulnerability in VaultWriter - file paths not validated against vault boundary

[merikari]

Hi, great project! I was doing a security review before deploying this as an MCP server against a personal vault, and found a path traversal issue worth flagging.

Location: src/lib/writer.ts — kg_create_node and kg_annotate_node tools

Issue: User-supplied directory and nodeId parameters are passed to path.join() without verifying the resolved absolute path stays within vaultPath. path.join() normalizes paths but does not block escape sequences like ../../.

Impact: A crafted tool call could potentially write files outside the intended vault directory.

Suggested fix:

const absPath = path.resolve(this.vaultPath, directory, filename);
const relative = path.relative(this.vaultPath, absPath);
if (relative.startsWith('..') || path.isAbsolute(relative)) {
  throw new Error(`Path escape attempt: ${absPath}`);
}

This check should be applied before any file creation or append operation in VaultWriter.