---
title: "CVE-2026-53512: Better Auth: OAuth refresh-token replay via missing client authentication on oidc-provider and mcp plugins"
url: https://erroneo.us/security/cve/CVE-2026-53512/
description: "CVE-2026-53512 (better-auth (npm)): Better Auth is an authentication and authorization library for TypeScript. Prior to 1.6.11, the legacy oidcProvider and…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-07-15
date_modified: 2026-07-20
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-53512"
kev: false
cvss: 9.1
epss: 0.00275
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-53512: Better Auth: OAuth refresh-token replay via missing client authentication on oidc-provider and mcp plugins

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.3% , percentile 19: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 19% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes better-auth (npm) < 1.6.11, fixed in 1.6.11 . Check your lockfile, including transitive dependencies.

## What it is

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 refreshtoken grant authenticates only possession of the bound refreshToken row and matching clientid, without verifying the confidential client's clientsecret, allowing an attacker with a valid refreshtoken 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 packages

- npm `better-auth` < 1.6.11 → fixed: 1.6.11

## Affected products (CVE record)

- better-auth better-auth: < 1.6.11

## Severity

- GitHub_M CVSS 4.0: 9.1 `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`
- GitHub CVSS 4.0: 9.1 `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`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.27% probability of exploitation activity in the next 30 days; percentile 19.

## Sources

- [GitHub Advisory GHSA-pw9m-5jxm-xr6h](https://github.com/advisories/GHSA-pw9m-5jxm-xr6h)
- [CVE.org record CVE-2026-53512](https://www.cve.org/CVERecord?id=CVE-2026-53512)
- [NVD entry CVE-2026-53512](https://nvd.nist.gov/vuln/detail/CVE-2026-53512)
- [github.com](https://github.com/better-auth/better-auth/security/advisories/GHSA-pw9m-5jxm-xr6h)
- [github.com](https://github.com/better-auth/better-auth/pull/9576)
- [github.com](https://github.com/better-auth/better-auth/commit/1f2ff4215c4affff0b140b0c0a712c0dde35659c)
- [github.com](https://github.com/better-auth/better-auth/releases/tag/v1.6.11)

---
Source page: https://erroneo.us/security/cve/CVE-2026-53512/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt