Grav: Unauthenticated Path Traversal via Missing Directory-Boundary Check in `plugin-asset-map.php` Static Asset Server (`index.php`)

**Verified against:** `getgrav/grav` devel branch, `GRAV_VERSION = "2.0.15"`, file `index.php ## Title Unauthenticated Path Traversal via Missing Directory-Boundary Check in `plugin-asset-map.php` Static Asset Server (`index.php`) ## Product / Affected Versions - Product: `getgrav/grav` - File: `index.php` (top-level front controller, runs before Grav itself boots) - Confirmed present in: devel branch, 2.0.15 - **Precondition:** requires `user/config/plugin-asset-map.php` to exist and contain at least one route-prefix mapping ,this is an opt-in mechanism (per the code comment: "Fast static asset serving for plugins that bundle SPA apps"). No core mechanism generates this file automatically; it's created by a plugin that opts into this fast-path. **Not reachable on a stock Grav install with no such plugin.** Where reachable, it requires zero authentication. ## CWE CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') , specific mechanism: a path-prefix containment check performed with plain string comparison (`str_starts_with`) instead of a directory-boundary-aware comparison, allowing escape into any sibling path whose name happens to extend the base directory's name as a string. ## Description `index.php` implements a fast-path static file server that runs *before* Grav's own routing/security stack, gated on the presence of an asset-map file: ```php $assetMapFile = __DIR__ . '/user/config/plugin-asset-map.php'; if (is_file($assetMapFile)) { $assetMap = require $assetMapFile; foreach ($assetMap as $routePrefix => $diskPath) { if (str_starts_with($path, $routePrefix)) { $relPath = substr($path, strlen($routePrefix)); $filePath = __DIR__ . '/' . ltrim($diskPath, '/') . $relPath; $realFile = realpath($filePath); $realBase = realpath(__DIR__ . '/' . ltrim($diskPath, '/')); if ($realFile && $realBase && str_starts_with($realFile, $realBase) && is_file($realFile)) { // ... serves $realFile directly, with Content-Type inferred from extension readfile($realFile); exit; } } } } ``` `realpath()` correctly resolves `..` sequences, so a naive `../../etc/passwd`-style traversal that leaves the filesystem entirely is blocked (it wouldn't share the `$realBase` string prefix). **But the containment check itself, `str_starts_with($realFile, $realBase)`, has no directory-boundary awareness** it's a plain string-prefix test, not "is `$realFile` inside the `$realBase` directory." Any resolved path whose string representation merely *begins with* the same characters as `$realBase` passes, including sibling directories that extend the base directory's name (`assets` → `assets-secret`, `assets.bak`, `assets_old`, `assets2`, etc.) a very common real-world directory-naming pattern (backup dirs, versioned dirs, disabled/legacy dirs sitting alongside the active one). ## Live Proof of Concept **Setup:** the exact code block above, extracted verbatim from `index.php`, executed with PHP 8.3.6 against a realistic directory layout (a plugin's active `assets/` dir sitting next to an unrelated `assets-secret/` dir containing a fake secret): ``` user/plugins/myplugin/assets/app.js <- intended, public user/plugins/myplugin/assets-secret/config.php <- NOT intended to be served user/config/plugin-asset-map.php: return ['/myplugin-assets' => 'user/plugins/myplugin/assets']; ``` **Legitimate request** (`/myplugin-assets/app.js`): ``` realFile: '/home/claude/grav-poc/user/plugins/myplugin/assets/app.js' realBase: '/home/claude/grav-poc/user/plugins/myplugin/assets' >>> WOULD SERVE FILE <<< >>> Content: public asset content ``` **Traversal request** (`/myplugin-assets/../assets-secret/config.php`): ``` realFile: '/home/claude/grav-poc/user/plugins/myplugin/assets-secret/config.php' realBase: '/home/claude/grav-poc/user/plugins/myplugin/assets' >>> WOULD SERVE FILE <<< >>> Content: SECRET_API_KEY=sk_live_totally_secret_12345 ``` `str_starts_with('.../assets-secret/config.php', '.../assets')` evaluates `true` because `assets-secret` literally begins with the characters `assets` there is no separator-boundary check (e.g. requiring `$realBase . '/'` as the actual prefix) to prevent this. ## Trust-boundary framing (per Grav's own SECURITY.md) This code path requires **no Grav account** , it runs before Grav even initializes, directly off the raw request path. Per Grav's own stated criteria: *"An unauthenticated attacker can achieve RCE, exfiltrate site data, or gain admin-equivalent control. No Grav account required"* → this matches the **CRITICAL** bar exactly, for any deployment where the `plugin-asset-map.php` mechanism is in active use. ## Suggested Fix Append a trailing directory separator before the prefix comparison, or use a proper containment check: ```php if ($realFile && $realBase && ( $realFile === $realBase || str_starts_with($realFile, $realBase . DIRECTORY_SEPARATOR) ) && is_file($realFile)) { ``` This is the standard fix for this exact bug class , ensuring the matched prefix ends exactly at a directory boundary, not partway through a longer sibling name.