Better Auth: OAuth refresh-token replay via missing client authentication on oidc-provider and mcp plugins

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Summary

CVECVE-2026-53512
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-15 18:16:47 UTC
Updated2026-07-15 20:29:17 UTC
DescriptionBetter 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.

Risk And Classification

Primary CVSS: v4.0 9.1 CRITICAL from [email protected]

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: 0.003030000 probability, percentile 0.222760000 (date 2026-07-16)

Problem Types: CWE-287 | CWE-306 | CWE-345 | CWE-863 | CWE-287 CWE-287: Improper Authentication | CWE-306 CWE-306: Missing Authentication for Critical Function | CWE-345 CWE-345: Insufficient Verification of Data Authenticity | CWE-863 CWE-863: Incorrect Authorization

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary9.1CRITICALCVSS: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/C...
4.0CNADECLARED9.1CRITICALCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
Present
Privileges Required
None
User Interaction
None
Confidentiality
High
Integrity
High
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Better-auth Better-auth affected < 1.6.11 Not specified

References

ReferenceSourceLinkTags
github.com/better-auth/better-auth/pull/9576 [email protected] github.com
github.com/better-auth/better-auth/commit/1f2ff4215c4affff0b140b0c0a712c... [email protected] github.com
github.com/better-auth/better-auth/releases/tag/v1.6.11 [email protected] github.com
github.com/better-auth/better-auth/security/advisories/GHSA-pw9m-5jxm-xr6h [email protected] github.com
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