liquidjs has a path traversal fallback vulnerability

liquidjs is a Shopify / GitHub Pages compatible template engine in pure JavaScript. Prior to 10.25.0, the layout, render, and include tags allow arbitrary file access via absolute paths (either as string literals or through Liquid variables, the latter require dynamicPartials: true, which is the default). This poses a security risk when malicious users are allowed to control the template content or specify the filepath to be included as a Liquid variable. This vulnerability is fixed in 10.25.0.

liquidjs is a Shopify / GitHub Pages compatible template engine in pure JavaScript. Prior to 10.25.0, the layout, render, and include tags allow arbitrary file access via absolute paths (either as string literals or through Liquid variables, the latter require dynamicPartials: true, which is the default). This poses a security risk when malicious users are allowed to control the template content or specify the filepath to be included as a Liquid variable. This vulnerability is fixed in 10.25.0.

liquidjs is a Shopify / GitHub Pages compatible template engine in pure JavaScript. Prior to 10.25.0, the layout, render, and include tags allow arbitrary file access via absolute paths (either as string literals or through Liquid variables, the latter require dynamicPartials: true, which is the default). This poses a security risk when malicious users are allowed to control the template content or specify the filepath to be included as a Liquid variable. This vulnerability is fixed in 10.25.0.

### Impact The `layout`, `render`, and `include` tags allow arbitrary file access via absolute paths (either as string literals or through Liquid variables, the latter require `dynamicPartials: true`, which is the default). This poses a security risk when malicious users are allowed to control the template content or specify the filepath to be included as a Liquid variable. ### Patches The root cause is LiquidJS allows `require.resolve()` as fallback but doesn't limit the directories it can resolve to. The issue is fixed via [#855](https://github.com/harttle/liquidjs/pull/855) and published version 10.25.0 on npm. ### Workarounds #### Change the files in build time In build time, through Shell script or Webpack `string-replace-loader`, change the file content of correxponding file (depending on your package `type`, for CommonJS it's `dist/liquid.node.js`) under `dist/`, ```diff if (fs.fallback !== undefined) { const filepath = fs.fallback(file) - if (filepath !== undefined) yield filepath + if (filepath !== undefined) { + for (const dir of dirs) { + if (!enforceRoot || this.contains(dir, filepath)) { + yield filepath + break + } + } } } ``` #### Overriding by `fs` LiquidJS option Adding a [`fs` option](https://liquidjs.com/api/interfaces/FS.html) to override the [default `fs` implementation](https://github.com/harttle/liquidjs/blob/1b85fdaa9c535021f7030a239a64003af26d31b5/src/fs/fs-impl.ts#L36-L40): ```javascript const { statSync, readFileSync, promises: { stat, readFile } } = require('fs') const { resolve, extname, dirname, sep } = require('path') const fs = { exists: async (fp) => { try { await stat(fp); return true; } catch { return false } }, existsSync: (fp) => { try { statSync(fp); return true } catch { return false } }, resolve: (root, file, ext) => resolve(root, file + (extname(file) ? '' : ext)), contains: (root, file) => { const r = resolve(root) return file.startsWith(r.endsWith(sep) ? r : r + sep) }, readFile: (fp) => readFile(fp, 'utf8'), readFileSync: (fp) => readFileSync(fp, 'utf8'), fallback: () => undefined, dirname, sep }; const engine = new Liquid({ fs }) ``` ### References Discussions: https://github.com/harttle/liquidjs/pull/851 Code fix: https://github.com/harttle/liquidjs/pull/855