CVE-2026-53518 Better Auth OAuth Provider: Race Condition in Authorization Code Exchange Enables Multi-Use Code Redemption

Better Auth is an authentication and authorization library for TypeScript. From 1.6.0 until 1.6.11, the @better-auth/oauth-provider POST /oauth2/token endpoint for the authorizationcode grant redeems a single-use authorization code through a non-atomic find-then-delete sequence, allowing two...

CVE-2026-53518

CVE-2026-53518 affects the Better Auth ecosystem, specifically the @better-auth/oauth-provider token endpoint for the authorization_code grant (and legacy paths via oidc-provider/mcp plugins). A race condition arises from a non-atomic find-then-delete when redeeming a single-use authorization cod...