CVE-2026-53517

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

State: Published
Severity: 8.1 High
Published: Jul 15, 2026
Updated: Jul 15, 2026
Reserved: Jun 9, 2026

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.

Scores

CVSS	Score	Vector	Source
3.1	8.1 High	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N	GitHub_M

Weaknesses

CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition

Affected Products

Product	Versions
better-authbetter-auth	>= 1.4.8-beta.7, < 1.6.0Affected
oauth-provider@better-auth	>= 1.6.0, < 1.6.11Affected

References

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