Thinkific Thinkific Online Course Creation Platform 1.0 is affected by: Cross Site Scripting (XSS). The impact is: execute arbitrary code (remote). The component is: Affected Source code of the website CMS which is been used by many to host their online courses using the Thinkific Platform. The attack vector is: To exploit the vulnerability any user has to just visit the link - https://hacktify.thinkific.com/account/billing?success=%E2%80%AA%3Cscript%3Ealert(1)%3C/script%3E. ¶¶ Thinkific is a Website based Learning Platform Product which is used by thousands of users worldwide. There is a Cross Site Scripting (XSS) based vulnerability in the code of the CMS where any attacker can execute a XSS attack. Proof of Concept & Steps to Reproduce: Step1 : Go to Google.com Step 2 : Search for this Dork site:thinkific.com -www Step 3 : You will get a list of websites which are running on the thinkific domains. Step 4 : Create account and signin in any of the website Step 5 : Add this endpoint at the end of the domain and you will see that there is a XSS Alert /account/billing?success=%E2%80%AA Step 6 : Choose any domains from google for any website this exploit will work on all the websites as it is a code based flaw in the CMS Step 7 : Thousands of websites are vulnerable due to this vulnerable code in the CMS itself which is giving rise to the XSS attack.