This cheat sheet was compiled by Dewhurst Security to record the knowledge gained when testing WordPress plugins for security issues for our clients. The security documentation provided by WordPress and found online for plugin security is sparse, outdated or unclear. This cheat sheet is intended for Penetration Testers who audit WordPress plugins or developers who wish to audit their own WordPress plugins.
This is a living document, feedback in the form of Issues or Pull Requests is very much welcomed.
Check if the following global PHP variables are echo'd to pages, or stored in the database and echo'd at a later time without first being sanitised or output encoded.
$_GET$_POST$_REQUEST$_SERVER['REQUEST_URI']$_SERVER['PHP_SELF']$_SERVER['HTTP_REFERER']$_COOKIE
(Note: the list of sources above is not extensive nor complete)
The following functions can cause XSS if not secured:
add_query_arg()remove_query_arg()
When doing dynamic testing for XSS the following setting in the wp-config.php file may reduce false positive results as it prevents administrative and editor users from being able to embed/execute JavaScript/HTML, which by default they are permitted to do.
define( 'DISALLOW_UNFILTERED_HTML', true );
Unsafe API methods (require sanitising/escaping):
$wpdb->query()$wpdb->get_var()$wpdb->get_row()$wpdb->get_col()$wpdb->get_results()$wpdb->replace()
Safe API methods (according to WordPress):
$wpdb->insert()$wpdb->update()$wpdb->delete()
Safe code, prepared statement:
<?php $sql = $wpdb->prepare( 'query' , value_parameter[, value_parameter ... ] ); ?>
Note: Before WordPress 3.5 $wpdb->prepare could be used insecurely as you could just pass the query without using placeholders, like in the following example:
$wpdb->query( $wpdb->prepare( "INSERT INTO table (user, pass) VALUES ('$user', '$pass')" ) );
Unsafe escaping ('securing') API methods:
esc_sql()function does not adequately protect against SQL Injection https://codex.wordpress.org/Function_Reference/esc_sqlescape()same as aboveesc_like()same as abovelike_escape()same as above
<?php $wpdb->show_errors(); ?>
<?php $wpdb->hide_errors(); ?>
<?php $wpdb->print_error(); ?>
is_admin()does not check if the user is authenticated as administrator, only checks if page displayed is in the admin section, can lead to auth bypass if misused.is_user_admin()same as abovecurrent_user_can()used for checking authorisation. This is what should be used to check authorisation.
wp_redirect()function can be used to redirect to user supplied URLs. If user input is not sanitised or validated this could lead to Open Redirect vulnerabilities.
wp_nonce_field()adds CSRF token to formswp_nonce_url()adds CSRF token to URLwp_verify_nonce()checks the CSRF token validity server sidecheck_admin_referer()checks the CSRF token validity server side and came from admin screen