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Critical, CVSS 9.1amended

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

CVE-2026-53512GHSA-pw9m-5jxm-xr6h

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (better-auth 1.6.11), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
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 · score source
EPSS
  • CVE-2026-53512: 0.27% estimated exploitation activity in the next 30 days; percentile 20.00 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Am I affected? Users are affected if all of the following are true: - Their application uses better-auth and has enabled at least one of: oidcProvider() (imported from better-auth/plugins/oidc-provider), or mcp() (imported from better-auth/plugins/mcp). - Their application has at least one confidential OAuth client registered (any client with type: "web" | "native" | "user-agent-based" in the oauthApplication table, or any trustedClients entry without type: "public"). Public clients with PKCE are not affected. - Their application uses better-auth at a version below the patched release. If an application only uses @better-auth/oauth-provider (the canonical replacement for oidc-provider) and the mcp plugin is not enabled, it is not affected. Fix: 1. Upgrade to better-auth@1.6.11 or later. 2. Migrate from the deprecated oidcProvider() to @better-auth/oauth-provider when feasible. The new package enforces client authentication on both grants by default. 3. If developers cannot upgrade…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 4 · amended ·

    Amended from ghsa record GHSA-pw9m-5jxm-xr6h

  2. Revision 3 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 2 · amended ·

    Amended from osv record GHSA-pw9m-5jxm-xr6h

  4. Revision 1 · created ·

    Published from ghsa record GHSA-pw9m-5jxm-xr6h

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-53512

Advisory: Better Auth: OAuth refresh-token replay via missing client authentication on oidc-provider and mcp plugins
IDs: CVE-2026-53512, GHSA-pw9m-5jxm-xr6h
Record: https://patchnext.com/advisories/cve-2026-53512 (revision 4, source checked 26 Oct 2026, 12:57 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: better-auth 1.6.11. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm better-auth: affected < 1.6.11; fixed in 1.6.11

## Suggested inspection (read-only)
- `npm ls better-auth --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on better-auth.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-pw9m-5jxm-xr6h (GitHub-reviewed advisory GHSA-pw9m-5jxm-xr6h lists affected ranges: npm better-auth >=0 <1.6.11)
- Verified: https://osv.dev/vulnerability/GHSA-pw9m-5jxm-xr6h (OSV record GHSA-pw9m-5jxm-xr6h lists affected ranges: npm better-auth >=0 <1.6.11 (fixed))

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