Escaping and sanitizing SVGs in metabox textarea

Here is a PHP library that was created for sanitizing SVG files that may be worth looking into. https://github.com/darylldoyle/svg-sanitizer

Here is an example of how this could be used:

// Now do what you want with your clean SVG/XML data

function your_save_meta( $post_id, $post, $update ) {

    // - Update the post's metadata.

    if ( isset( $_POST['svg_meta'] ) ) {

        // Load the sanitizer. (This path will need to be updated)
        use enshrined\svgSanitize\Sanitizer;

        // Create a new sanitizer instance
        $sanitizer = new Sanitizer();

        // Pass your meta data to the sanitizer and get it back clean
        $cleanSVG = $sanitizer->sanitize($_POST['svg_meta']);

        // Update your post meta
        update_post_meta( $post_id, 'svg_meta_name', $cleanSVG );

    }

}
add_action( 'save_post', 'your_save_meta', 10, 3 );