CVE-2025-29927: Next.js middleware authorization bypass checklist

CVE-2025-29927 is the Next.js middleware authorization bypass advisory published on March 21, 2025. It remains relevant to older deployments and inherited applications, even though it is not a newly disclosed vulnerability. The security question is whether the application enforces permissions at the point where protected data or actions are accessed.

Historical affected versions and fixes

The vendor advisory covers versions from 11.1.4 before 12.3.5, 13.0.0 before 13.5.9, 14.0.0 before 14.2.25, and 15.0.0 before 15.2.3. It describes authorization checks in middleware being bypassed. Fixes were released as 12.3.5, 13.5.9, 14.2.25 and 15.2.3. The advisory states Vercel-hosted deployments were automatically protected. Its fallback mitigation blocks external requests carrying the x-middleware-subrequest header from reaching the application.

A login redirect is not the whole permission model

Inventory what each protected area actually does. A dashboard can load several APIs, download files and submit changes independently of its initial page request. For every sensitive operation, identify where the application checks the caller's identity and whether that identity is allowed to access the requested resource. Include server-side handlers used by background workflows and mobile clients.

Create a small permission matrix with the resources as rows and the intended user roles as columns. Add an unauthenticated state and a signed-in user belonging to a different organization where relevant. This makes expected behavior explicit before anyone interprets a test result. It also exposes cases where the team has never agreed who should have access.

Verify access with authorized test accounts

1. Use dedicated test accounts representing the roles in the permission matrix. Keep production customer data out of the exercise wherever possible.
2. Check the protected operation itself, including relevant APIs and downloads, rather than relying only on whether a menu item is visible.
3. Record the expected result and observed result for each role. An application error is not automatically a successful denial; inspect whether sensitive data or a state change occurred.
4. Review denied requests in application logs so developers can distinguish intentional access control from unrelated failures.
5. Retest the same permission cases after the framework upgrade and any authorization changes.

Patch old deployments without stopping at an old minimum

The versions above describe the historical fix for this advisory. Select a currently supported release that includes other applicable security updates. Check the installed dependency in the deployed artifact, then confirm the running service uses that artifact. Include old previews and customer-specific installations in the rollout; a patched primary domain does not update them automatically.

Document hosting mitigations separately from application updates. If a team relies on an upstream protection, record which traffic path it covers and who owns that control. The release record should still identify the application version. This avoids confusion when hosting, routing or provider arrangements change later.

For longer-term maintenance, keep permission checks close to the sensitive operation and preserve the permission matrix as the product adds roles. A security review becomes much more concrete when it can compare observed behavior with an agreed access rule instead of guessing from the interface.

Use MyPentest on your authorized website to review supported checks and actionable findings. Specific coverage for CVE-2025-29927 is not confirmed here. Pair scanning with deployed-version verification and a scoped access-control review; untested roles and operations remain unknown.