CVE-2025-27143: better auth Open Redirect — Fix

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.

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CVSS v3.1 Score

6.1

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Weakness Type (CWE)

CWE-601 CWE-601

Affected Products

Vendor	Product	Versions
better-auth	better_auth	< 1.1.21

References

Advisories & Patches

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/security/advisories/GHSA-hjpm-7mrm-26w8

Other References

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

Frequently Asked Questions

What is CVE-2025-27143? +

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. It has a CVSS v3.1 base score of 6.1 (MEDIUM).

How severe is CVE-2025-27143? +

CVE-2025-27143 has a CVSS v3.1 score of 6.1 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-27143? +

CVE-2025-27143 affects products from better-auth, specifically: better_auth. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-27143? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2025-27143