CVE-2026-53518 Better Auth OAuth Provider: Race Condition in Authorization Code Exchange Enables Multi-Use Code Redemption
Concurrent requests can redeem a single-use OAuth authorization code multiple times, allowing attackers to mint duplicate tokens and potentially take over accounts.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-53518?
CVE-2026-53518 is a high-severity vulnerability in better-auth, published on 15 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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 authorization_code grant redeems a single-use authorization code through a non-atomic find-then-delete sequence, allowing two concurrent requests to pass the read step and mint independent access tokens, refresh tokens, and ID tokens; legacy /oauth2/token and /mcp/token paths in oidc-provider and mcp plugins share the same primitive. This issue is fixed in version 1.6.11.
Which versions are affected by CVE-2026-53518?
4 open source packages ship an affected version, including @better-auth/oauth-provider and better-auth. It affects 2 products.
| Package | Affected | Fixed in |
|---|---|---|
@better-auth/oauth-provider npm | From 1.6.0 | 1.6.11 |
@better-auth/oauth-provider npm | From 1.6.0 | 1.6.11 |
better-auth npm | All versions | 1.6.11 |
better-auth npm | All versions | 1.6.11 |
Products include Better-Auth Better-Auth\/Oauth-Provider, Better-Auth Better Auth.
How do I fix CVE-2026-53518?
Upgrade @better-auth/oauth-provider to 1.6.11 or later.
Is CVE-2026-53518 being exploited?
There is no known exploitation of CVE-2026-53518 in the wild and no public exploit code.
Other vulnerabilities in better-auth
Sources
Also known as GHSA-7w99-5wm4-3g79.