What’s Vulnerable › Vulnerabilities

CVE-2025-27143: Beter Auth has an Open Redirect via Scheme-Less Callback Parameter

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-02-24 · updated 2026-06-17
• Weakness: CWE-601

Description

Better Auth is an authentication and authorization library for TypeScript. Prior to version 1.1.21, 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 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. This CVE is a bypass of the fix for GHSA-8jhw-6pjj-8723/CVE-2024-56734. Version 1.1.21 contains an updated patch.

Affected products

• better-auth: before 1.1.21 — fixed in 1.1.21

How to fix

Upgrade to a fixed version: better-auth 1.1.21. Check the vendor advisory for mitigations.

References

• https://github.com/better-auth/better-auth/commit/24659aefc35a536b95ea4e5347e52c8803910153
• https://github.com/better-auth/better-auth/commit/b381cac7aafd6aa53ef78b6ab771ebfa24643c80
• https://github.com/better-auth/better-auth/releases/tag/v1.1.21
• https://github.com/better-auth/better-auth/security/advisories/GHSA-8jhw-6pjj-8723
• https://github.com/better-auth/better-auth/security/advisories/GHSA-hjpm-7mrm-26w8

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