# CVE-2026-53517: Better Auth OAuth Provider: Refresh Token Rotation Race Condition Allows Concurrent Replay and Token Family Forking

> Concurrent requests can fork refresh token families, allowing attackers to bypass token revocation and maintain unauthorized access.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Jul 2026
- **Updated:** 15 Jul 2026
- **Also known as:** GHSA-392p-2q2v-4372

## What is CVE-2026-53517?

CVE-2026-53517 is a high-severity vulnerability in @better-auth better-auth, published on 15 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Better Auth is an authentication and authorization library for TypeScript. From 1.4.8-beta.7 until 1.6.11, the @better-auth/oauth-provider POST /oauth2/token endpoint on the refresh_token grant performs a non-atomic read, validate, revoke, and mint sequence on the oauthRefreshToken row, allowing concurrent requests with the same parent refresh token to pass the revoked check and create forked refresh-token families; the vulnerable range also includes embedded better-auth plugin versions before 1.6.0. This issue is fixed in version 1.6.11.

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition), CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-53517?

4 open source packages ship an affected version, including @better-auth/oauth-provider and better-auth. It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@better-auth/oauth-provider` | npm | From 1.6.0 | 1.6.11 |
| `@better-auth/oauth-provider` | npm | From 1.6.0 | 1.6.11 |
| `better-auth` | npm | From 1.4.8-beta.7 | 1.6.0 |
| `better-auth` | npm | From 1.4.8-beta.7 | 1.6.0 |

Products: Better-Auth Better-Auth\/Oauth-Provider, Better-Auth Better Auth.

## How do I fix CVE-2026-53517?

Upgrade @better-auth/oauth-provider to 1.6.11 or later.

## Is CVE-2026-53517 being exploited?

There is no known exploitation of CVE-2026-53517 in the wild and no public exploit code.

## Other vulnerabilities in @better-auth better-auth

- [CVE-2026-53518](https://insights.sbomify.com/CVE-2026-53518/): Better Auth OAuth Provider: Race Condition in Authorization Code Exchange Enables Multi-Use Code Redemption (high 7.6)
- [CVE-2026-41427](https://insights.sbomify.com/CVE-2026-41427/): Better Auth OAuth 2.1 Provider: Unprivileged users can register OAuth clients (high 7.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-53517 and fix it if it is affected.

What it is: CVE-2026-53517 is a high-severity vulnerability in @better-auth better-auth, published on 15 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-53517 in the wild and no public exploit code.

Affected packages and fixed versions:
- @better-auth/oauth-provider (npm): affected from 1.6.0; fixed in 1.6.11
- @better-auth/oauth-provider (npm): affected from 1.6.0; fixed in 1.6.11
- better-auth (npm): affected from 1.4.8-beta.7; fixed in 1.6.0
- better-auth (npm): affected from 1.4.8-beta.7; fixed in 1.6.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-53517/ (Markdown: https://insights.sbomify.com/CVE-2026-53517/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53517
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53517
- OSV: https://osv.dev/vulnerability/CVE-2026-53517

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53517/
Summaries are generated and may contain mistakes; the official description above is the record.