Craft is a content management system (CMS). A vulnerability in CraftCMS allows an attacker to bypass local file system validation by utilizing a double file:// scheme (e.g., file://file:////). This enables the attacker to specify sensitive folders as the file system, leading to potential file overwriting through malicious uploads, unauthorized access to sensitive files, and, under certain conditions, remote code execution (RCE) via Server-Side Template Injection (SSTI) payloads. Note that this will only work if you have an authenticated administrator account with allowAdminChanges enabled. This is fixed in 5.4.6 and 4.12.5.

Affected: Packagist: craftcms/cms

### Summary A vulnerability in CraftCMS allows an attacker to bypass local file system validation by utilizing a double `file://` scheme (e.g., `file://file:////`). This enables the attacker to specify sensitive folders as the file system, leading to potential file overwriting through malicious uploads, unauthorized access to sensitive files, and, under certain conditions, remote code execution (RCE) via Server-Side Template Injection (SSTI) payloads.

Note that this will only work if you have an authenticated administrator account with [allowAdminChanges enabled](https://craftcms.com/docs/5.x/reference/config/general.html#allowadminchanges).

https://craftcms.com/knowledge-base/securing-craft#set-allowAdminChanges-to-false-in-production

### Details The issue lies in line 57 of `cms/src/helpers/FileHelper.php`, it only removes `file://` on the most left. It is trivial to bypass this sanitization by adding 2 `file://`, e.g. `file://file:////`. ```php public static function normalizePath($path, $ds = DIRECTORY_SEPARATOR): string { // Remove any file protocol wrappers $path = StringHelper::removeLeft($path, 'file://');

// Is this a UNC network share path? $isUnc = (str_starts_with($path, '//') || str_starts_with($path, '\\\\'));

// Normalize the path $path = parent::normalizePath($path, $ds);

// If it is UNC, add those slashes back in front if ($isUnc) { $path = $ds . $ds . ltrim($path, $ds)…