CVE-2026-53517: Better Auth OAuth Provider: Refresh Token Rotation Race Condition Allows Concurrent Replay and Token Family Forking

Description

Better Auth is an authentication and authorization library for TypeScript. From 1.4.8-beta.7 until 1.6.11, the @better-auth/oauth-provider POST /oauth2/token endpoint on the refresh_token grant performs a non-atomic read, validate, revoke, and mint sequence on the oauthRefreshToken row, allowing concurrent requests with the same parent refresh token to pass the revoked check and create forked refresh-token families; the vulnerable range also includes embedded better-auth plugin versions before 1.6.0. This issue is fixed in version 1.6.11.

CVSS vector

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

Attack vector

Network

Complexity

Low

Privileges

Low

User interaction

None

Confidentiality

High

Integrity

High

Availability

None

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)0.4% · higher than 36% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

BE

better-auth · better-auth

>= 1.4.8-beta.7, < 1.6.0 · source: vendor

OA

oauth-provider · @better-auth

>= 1.6.0, < 1.6.11 · source: vendor

BA

Better Auth · Better-auth

1.4.9 before 1.6.11; 1.4.8; 1.4.8 · source: NVD

BE

Better-auth/oauth-provider · Better-auth

1.6.0 before 1.6.11 · source: NVD