Better Auth has stored XSS in the auth-server origin via javascript: redirect_uri in oidc-provider and mcp

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.7 · CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:N

EPSS

• CVE-2026-67333: 0.26% estimated exploitation activity in the next 30 days; percentile 18.25 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Am I affected? Check each condition. Users are affected when all of the first three hold. - Their application enables the oidc-provider plugin or the mcp plugin from better-auth/plugins. The mcp plugin wraps the same provider and carries the same defect. Both are on the migration path to @better-auth/oauth-provider, which is not affected. - Their application better-auth version is 1.6.12 or earlier on the stable line, or any 1.7.0-beta build on the pre-release line. Both release lines carry the same defect. - Their application consent page is a client component that reads redirectURI from the authClient.oauth2.consent(...) response and assigns it to a browser navigation target such as window.location.href, location.assign, or location.replace. Two conditions raise an application's exposure: - It sets allowDynamicClientRegistration: true. Client registration is then unauthenticated, so any visitor can plant the malicious client. The default is false, which limits planting to…

Published by the source

7 Jul 2026, 20:55 UTC

Last modified by the source

2 Aug 2026, 03:56 UTC

Source last checked

26 Oct 2026, 12:56 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-86j7-9j95-vpqj

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-86j7-9j95-vpqj

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# Patch Next advisory brief: CVE-2026-67333

Advisory: Better Auth has stored XSS in the auth-server origin via javascript: redirect_uri in oidc-provider and mcp
IDs: CVE-2026-67333, GHSA-86j7-9j95-vpqj
Record: https://patchnext.com/advisories/cve-2026-67333 (revision 2, source checked 26 Oct 2026, 12:56 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: better-auth 1.7.0-beta.4, 1.6.13. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm better-auth: affected < 1.6.13; >= 1.7.0-beta.0, < 1.7.0-beta.4; fixed in 1.6.13, 1.7.0-beta.4

## 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://osv.dev/vulnerability/GHSA-86j7-9j95-vpqj (OSV record GHSA-86j7-9j95-vpqj lists affected ranges: npm better-auth >=0 =1.7.0-beta.0 <1.7.0-beta.4 (fixed))
- Verified: https://github.com/advisories/GHSA-86j7-9j95-vpqj (GitHub-reviewed advisory GHSA-86j7-9j95-vpqj lists affected ranges: npm better-auth >=0 =1.7.0-beta.0 <1.7.0-beta.4)

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