What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 8.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-15 · updated 2026-07-21
• Weakness: CWE-362

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.

Affected products

• Better-Auth/Oauth-Provider: from 1.6.0 before 1.6.11 — fixed in 1.6.11
• better-auth: from 1.6.0 before 1.6.11 — fixed in 1.6.11

How to fix

Upgrade to a fixed version: Better-Auth/Oauth-Provider 1.6.11; better-auth 1.6.11. Check the vendor advisory for mitigations.

References

• https://github.com/better-auth/better-auth/commit/b4bc65a007784b2eb0efb459e5fa6fd8055d3ec9
• https://github.com/better-auth/better-auth/releases/tag/v1.6.11
• https://github.com/better-auth/better-auth/security/advisories/GHSA-7w99-5wm4-3g79

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