Shivaraj-Kolekar

**Name of the Vulnerable Software and Affected Versions** Better Auth versions prior to 1.1.21 **Description** The application is vulnerable to an open redirect due to improper validation of the `callbackURL` parameter in the email verification endpoint and any other endpoint that accepts a callback URL. While the server blocks fully qualified URLs, it incorrectly allows scheme-less URLs. This results in the browser interpreting the URL as a fully qualified URL, leading to unintended redirection. An attacker can exploit this flaw by crafting a malicious verification link and tricking users into clicking it. Upon successful email verification, the user will be automatically redirected to the attacker's website, which can be used for phishing, malware distribution, or stealing sensitive authentication tokens. **Recommendations** Upgrade to Better Auth version 1.1.21 or later to enforce domain validation for `callbackURL` for the `/verify-email` path and for all other `GET` endpoints. As a temporary workaround, consider using hooks to pre-check URLs in your auth instance to prevent this without upgrading, by checking if the `callbackURL` is a trusted callback URL or not in the `before` hook.