AzuraCast is a self-hosted, all-in-one web radio management suite. Prior to version 0.23.6, the currentDirectory request parameter in the Flow.js media upload endpoint (POST /api/station/{station_id}/files/upload) is not sanitized for path traversal sequences. When combined with a local filesystem storage backend (the default), an authenticated user with media management permissions can write arbitrary files outside the station's media storage directory, achieving remote code execution by writing a PHP webshell to the web root. This issue has been patched in version 0.23.6.

Affected: Packagist: azuracast/azuracast

## Summary

The `currentDirectory` request parameter in the Flow.js media upload endpoint (`POST /api/station/{station_id}/files/upload`) is not sanitized for path traversal sequences. When combined with a local filesystem storage backend (the default), an authenticated user with media management permissions can write arbitrary files outside the station's media storage directory, achieving remote code execution by writing a PHP webshell to the web root.

## Details

In `backend/src/Controller/Api/Stations/Files/FlowUploadAction.php`, the `currentDirectory` parameter is read directly from user input at line 79 and prepended to the sanitized filename at line 83:

```php // FlowUploadAction.php:79-84 $currentDir = Types::string($request->getParam('currentDirectory'));

$destPath = $flowResponse->getClientFullPath(); if (!empty($currentDir)) { $destPath = $currentDir . '/' . $destPath; } ```

While `$flowResponse->getClientFullPath()` is sanitized via `UploadedFile::filterClientPath()` (which strips `..` segments), the `$currentDir` value is prepended **after** this sanitization, reintroducing traversal capability.

This `$destPath` is passed to `MediaProcessor::processAndUpload()` at line 95-98. The critical issue is in the `finally` block at `backend/src/Media/MediaProcessor.php:114-117`:

```php // MediaProcessor.php:75-117 try { if (MimeType::isFileProcessable($localPath)) { // ... process media ... return $record; } // ... throw CannotPro…