WordPress Yoast SEO Cross Site Scripting
Posted on 22 November 2017
Discoverer: Elias Dimopoulos Linkedin: https://gr.linkedin.com/in/dimopouloselias Vulnerability: Reflected XSS Affected plugin: Yoast SEO plugin < 5.8.0 Active installations: 5+ million URL: https://wordpress.org/plugins/wordpress-seo/#developers Assigned CVE: CVE-2017-16842 ----------------------------------------------------------- Thanks Yoast for their immediate response. ----------------------------------------------------------- The vulnerability lies in the "tab" parameter and can cause reflected XSS vulnerability. The vulnerability can be exploited against an administrator by using the following url: http://victim/wp-admin/admin.php?page=wpseo_search_console&tab=settings'><script>alert(window.location)</script><!-- The victim has to have a valid profile under http://victim/wp-admin/admin.php?page=wpseo_search_console&tab=settings (example: profile.png) If there is the message "No profiles found" under the above link, the plugin has not finished with the configuration and the vulnerability cannot be exploited. A logged in Administrator, who will click on the above link, he will receive an alert box with the value of "window.location". In this case, the javascript code is just an alert box, however any kind of malicious javascript code can be used. Reproduce: 1. Login to your wordpress as an admin. 2. Ensure that a valid profile has been configured under http://victim/wp-admin/admin.php?page=wpseo_search_console&tab=settings (example: profile.png) 3. Access the following link: http://victim/wp-admin/admin.php?page=wpseo_search_console&tab=settings'><script>alert(window.location)</script><!-- 4. The alert box should be executed. The vulnerability has been tested against: * Yoast SEO Version: 5.7.1 * WordPress 4.8.3 running Twenty Seventeen theme. * Firefox 56.0 (64-bit) - Mozilla Firefox for Ubuntu canonical - 1.0 I also tried to track down the issue in the source code: file: admin/google_search_console/class-gsc-platform-tabs.php: 70 private function set_current_tab( array $platforms ) { 71 $this->current_tab = key( $platforms ); 72 if ( $current_platform = filter_input( INPUT_GET, 'tab' ) ) { 73 $this->current_tab = $current_platform; 74 } 75 } file: wordpress-seo/admin/google_search_console/class-gsc-table.php: 361 echo "<input id='field_platform' type='hidden' name='platform' value='{$platform}' />"; the filter_input function has the following definition: mixed filter_input ( int $type , string $variable_name [, int $filter = FILTER_DEFAULT [, mixed $options ]] ) If filter is omitted like in the code above, FILTER_DEFAULT will be used, which is equivalent to FILTER_UNSAFE_RAW. This will result in no filtering taking place by default. (ref: http://php.net/manual/en/function.filter-input.php)
