Description
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.
Affected products
better-auth: better auth
References4
- github.com/better-auth/better-auth/security/advisories/GHSA-pw9… MitigationVendor Advisory
- github.com/better-auth/better-auth/commit/1f2ff4215c4affff0b140… Patch
- github.com/better-auth/better-auth/pull/9576 Issue TrackingPatch
- github.com/better-auth/better-auth/releases/tag/v1.6.11 Release Notes
Metrics
- CVSS 3.1
-
9.1
CRITICAL
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N - CVSS 4.0
-
9.1
CRITICAL
Score source: CNA
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 0% percentile: 20 · as of 15 November 2026
- CWE
- CWE-287CWE-306CWE-345CWE-863
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.