CRITICAL: CVE-2026-53512 (CVSS 9.1) — better-auth better auth

CVE: CVE-2026-53512

CVSS: 9.1 (3.1) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Severity: CRITICAL

Status: Critical advisory

Affected

• better-auth better auth

Summary

Better Auth is an authentication and authorization library for TypeScript. Prior to 1.6.11, the legacy oidcProvider and mcp plugins expose OAuth token endpoints whose refresh_token grant authenticates only possession of the bound refreshToken row and matching client_id, without verifying the confidential client's client_secret, allowing an attacker with a valid refresh_token to mint access tokens and rotated refresh tokens through /api/auth/oauth2/token or /api/auth/mcp/token. The @better-auth/oauth-provider package is not affected. This issue is fixed in version 1.6.11.

Verified Sources

• NVD entry
• GitHub Advisory
• MITRE

References

• https://github.com/better-auth/better-auth/commit/1f2ff4215c4affff0b140b0c0a712c0dde35659c
• https://github.com/better-auth/better-auth/pull/9576
• https://github.com/better-auth/better-auth/releases/tag/v1.6.11
• https://github.com/better-auth/better-auth/security/advisories/GHSA-pw9m-5jxm-xr6h

_Validated by the Lyrie Threat Intelligence Pipeline — 3 independent sources confirmed before publication. No speculation._