Source

File: wp-includes/ms-load.php

function wp_get_active_network_plugins() {
	$active_plugins = (array) get_site_option( 'active_sitewide_plugins', array() );
	if ( empty( $active_plugins ) ) {
		return array();
	}

	$plugins        = array();
	$active_plugins = array_keys( $active_plugins );
	sort( $active_plugins );

	foreach ( $active_plugins as $plugin ) {
		if ( ! validate_file( $plugin )                     // $plugin must validate as file.
			&& '.php' === substr( $plugin, -4 )             // $plugin must end with '.php'.
			&& file_exists( WP_PLUGIN_DIR . '/' . $plugin ) // $plugin must exist.
			) {
			$plugins[] = WP_PLUGIN_DIR . '/' . $plugin;
		}
	}

	return $plugins;
}