better-auth Better Auth up to 1.6.10 OIDC Provider/MCP /api/auth/oauth2/token refresh_token improper authorization

Summaryinfo

A vulnerability identified as problematic has been detected in better-auth Better Auth up to 1.6.10. This issue affects some unknown processing of the file /api/auth/oauth2/token of the component OIDC Provider/MCP. This manipulation of the argument refresh_token causes improper authorization. The identification of this vulnerability is CVE-2026-53512. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in better-auth Better Auth up to 1.6.10. It has been declared as problematic. Affected by this vulnerability is some unknown functionality of the file /api/auth/oauth2/token of the component OIDC Provider/MCP. The manipulation of the argument refresh_token with an unknown input leads to a improper authorization vulnerability. The CWE definition for the vulnerability is CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. As an impact it is known to affect confidentiality. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-53512 since 06/09/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1548.002 according to MITRE ATT&CK.

Upgrading to version 1.6.11 eliminates this vulnerability.

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Productinfo

Vendor

• better-auth

Name

• Better Auth

Version

• 1.6.0
• 1.6.1
• 1.6.2
• 1.6.3
• 1.6.4
• 1.6.5
• 1.6.6
• 1.6.7
• 1.6.8
• 1.6.9
• 1.6.10

CPE 2.3info

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