Ghost 5.2.0 before 6.62.0 Unauthenticated Stripe Checkout Account Modification

Ghost versions 5.2.0 through versions prior to 6.62.0 allow a remote attacker, without authentication, to abuse the Stripe Checkout flow to attach a paid subscription to an existing member, modify that member's name, and inject content into newsletters sent to the member. Depending on the recipient's email client, the injected content may be rendered, resulting in HTML injection or cross-site scripting (XSS).