I have this code snippet: $design_file_path = APP_ROOT . '/templates/themes/' . $design . '.php'; Could an attacker enter something into $design to access non-php files or am I good? I'm talking specifically about non-php files. What would an attack

In the provided code snippet: ```php $design_file_path = APP_ROOT . '/templates/themes/' . $design . '.php'; ``` The `design` variable is concatenated to create a file path, which could pose a security risk if `$design` is not properly validated or sanitized. An attacker might exploit this by crafting a value for `$design` that points to a file outside of the intended directory. For instance, if there are no checks in place, an attacker might use directory traversal techniques, such as including `../`, to access files outside of the intended theme directory. ### Example Attack An attacker could set `$design` to: ``` ../../some/other/directory/config.txt ``` This would result in: ``` $design_file_path = APP_ROOT . '/templates/themes/' . '../../some/other/directory/config.txt.php'; ``` However, because of the `.php` extension being forced, the actual file being addressed becomes: ``` /path/to/app/templates/themes/../../some/other/directory/config.txt.php ``` If the server is configured to allow execution of this file, or if it has a .php handler that executes even if the file is a text file with a .php extension, the user could potentially access the contents of `config.txt` which may contain sensitive information. ### Mitigation To mitigate this risk, you should: 1. **Whitelist Valid Inputs**: Only allow a predefined list of values for `$design` that correspond to valid themes. For example, if your themes are `theme1`, `theme2`, etc., only accept those values. 2. **Validation**: Ensure that, irrespective of user input, the value of `$design` does not contain characters like `..`, `/`, or other potentially harmful sequences. 3. **Use a Defined Path**: Instead of directly constructing the file path from user input, consider defining the paths in a mapping array and retrieving the file based on a trusted key. 4. **Error Handling**: Implement error checks to handle non-existent files or unauthorized accesses gracefully rather than leaking file system structure or errors. 5. **File System Permissions**: Ensure your file system permissions are properly configured so that web server processes can't read sensitive files, even if they manage to reference them. By implementing these measures, you can significantly reduce the risk of an attacker exploiting the input for unauthorized file access.