Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS) in Pay

Impact
A payments info page of Pay is susceptible to reflected Cross-site
scripting. An attacker could create a working URL that renders a
javascript link to a user on a Rails application that integrates
Pay. This URL could be distributed via email to specifically target
certain individuals. If the targeted application contains a
functionality to submit user-generated content (such as comments)
the attacker could even distribute the URL using that functionality.
Patches
This has been patched in version 6.3.2 and above.
Pay will now sanitize the back parameter and only permit relative paths.