CVE-2026-53512

Better Auth: OAuth refresh-token replay via missing client authentication on oidc-provider and mcp plugins

State: Published
Severity: 9.1 Critical
Published: Jul 15, 2026
Updated: Jul 18, 2026
Reserved: Jun 9, 2026

Description

Better Auth is an authentication and authorization library for TypeScript. Prior to 1.6.11, the legacy oidcProvider and mcp plugins expose OAuth token endpoints whose refresh_token grant authenticates only possession of the bound refreshToken row and matching client_id, without verifying the confidential client's client_secret, allowing an attacker with a valid refresh_token to mint access tokens and rotated refresh tokens through /api/auth/oauth2/token or /api/auth/mcp/token. The @better-auth/oauth-provider package is not affected. This issue is fixed in version 1.6.11.

Scores

CVSS	Score	Vector	Source
4.0	9.1 Critical	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N	GitHub_M

Weaknesses

CWE-287 Improper Authentication
CWE-306 Missing Authentication for Critical Function
CWE-345 Insufficient Verification of Data Authenticity
CWE-863 Incorrect Authorization

Affected Products

Product	Versions
better-authbetter-auth	< 1.6.11Affected

References

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