CVE-2025-53535 in Better Auth
Summary
by MITRE • 07/07/2025
Better Auth is an authentication and authorization library for TypeScript. An open redirect has been found in the originCheck middleware function, which affects the following routes: /verify-email, /reset-password/:token, /delete-user/callback, /magic-link/verify, /oauth-proxy-callback. This vulnerability is fixed in 1.2.10.
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Analysis
by VulDB Data Team • 07/07/2025
The vulnerability identified as CVE-2025-53535 affects Better Auth, a TypeScript authentication and authorization library that provides essential security functions for web applications. This issue manifests as an open redirect vulnerability within the originCheck middleware function, which is a critical component responsible for validating the origins of authentication requests. The flaw specifically impacts several key authentication routes including email verification, password reset, user deletion confirmation, magic link verification, and OAuth proxy callbacks, making it particularly dangerous as it can affect the entire authentication flow of applications using this library.
The technical implementation of this vulnerability stems from insufficient validation of redirect URLs within the originCheck middleware, which allows malicious actors to manipulate the redirect behavior during authentication processes. When users are directed to authentication endpoints such as /verify-email or /reset-password/:token, the middleware fails to properly validate that the target URL originates from a trusted source, creating an opportunity for attackers to redirect users to malicious domains. This type of vulnerability maps directly to CWE-601, which specifically addresses open redirect vulnerabilities where applications redirect users to untrusted websites. The flaw represents a significant weakness in the library's input validation mechanisms and demonstrates poor secure coding practices in URL handling.
The operational impact of this vulnerability extends far beyond simple inconvenience, as it can enable sophisticated phishing attacks and credential theft operations. Attackers can exploit the open redirect to craft deceptive links that appear legitimate but redirect users to attacker-controlled domains, potentially capturing login credentials or other sensitive information. The affected routes are particularly concerning because they represent critical points in the user authentication lifecycle where users are most likely to trust the application's navigation and where sensitive actions occur. This vulnerability directly aligns with attack techniques described in the ATT&CK framework under T1566, which covers phishing campaigns that leverage open redirect vulnerabilities to redirect users to malicious sites. The potential for abuse increases significantly when considering that these routes are typically accessed during sensitive user operations such as password resets or account verification.
Organizations using Better Auth versions prior to 1.2.10 face substantial risk of exploitation, particularly those handling sensitive user data or operating in regulated environments where authentication security is paramount. The vulnerability creates a pathway for attackers to perform user impersonation, conduct credential harvesting attacks, or redirect users to sites that can harvest session tokens and other authentication artifacts. Security teams should immediately assess their applications for potential exposure and implement mitigation strategies including updating to the fixed version 1.2.10, implementing additional validation layers, and monitoring for suspicious redirect patterns in their application logs. The fix in version 1.2.10 addresses the core validation issue by ensuring that all redirect URLs are properly validated against a whitelist of trusted origins, thereby preventing unauthorized redirection during critical authentication flows.