CVE-2026-39859

Description

`liquidjs` 10.25.0 documents `root` as constraining filenames passed to `renderFile()` and `parseFile()`, but top-level file loads do not enforce that boundary. The published npm package `[email protected]` on Linux 6.17.0 with Node v22.22.1. A `Liquid` instance configured with an empty temporary directory as `root` still returned the contents of `/etc/hosts` when `renderFile('/etc/hosts')` was called. I have not exhaustively checked older releases yet; 10.25.0 is the latest tested version. Root cause: - `src/parser/parser.ts:83-85` calls `loader.lookup(file, LookupType.Root, ...)` and then reads the returned file. - `src/fs/loader.ts:38` passes `type !== LookupType.Root` into `candidates()`. - For `LookupType.Root`, `enforceRoot` is false, so `src/fs/loader.ts:47-66` accepts resolved absolute paths and fallback results without any `contains()` check. This appears adjacent to the March 10, 2026 fix for CVE-2026-30952, which hardened `include` / `render` / `layout` but not the top-level file-loading APIs. Proof of concept: ```javascript const fs = require('fs'); const os = require('os'); const path = require('path'); const { Liquid } = require('liquidjs'); const safeRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'liquidjs-safe-root-')); const engine = new Liquid({ root: [safeRoot], extname: '.liquid' }); engine.renderFile('/etc/hosts').then(console.log); ``` Expected result: a path outside `root` should be rejected. Actual result: `/etc/hosts` is rendered successfully. Impact: any application that treats `root` as a sandbox boundary and forwards attacker-controlled template names into `renderFile()` or `parseFile()` can disclose arbitrary local files readable by the server process. Suggested fix: apply the same containment checks used for partial/layout lookups to `LookupType.Root`, and reject absolute or fallback paths unless they remain within an allowed root. A regression test should verify that `renderFile('/etc/hosts')` fails when `root` points to an unrelated directory.

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