# CVE-2026-45109: Vercel Next.js authentication bypass in middleware with Turbopack

Source: https://junglewise.ai/threats/cve-2026-45109-vercel-next-js-authentication-bypass-in-middleware-with-turbopack  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-13. Updated: 2026-09-24  
License: CC BY 4.0 with a link back

CVE-2026-45109 · Severity: high · CVSS 7.5 · Published 2026-05-13

Next.js is a popular React framework used to build web applications. A previous security fix for middleware-based access controls in App Router applications was incomplete when using Turbopack, allowing attackers to bypass authentication and authorization checks to access protected routes. This affects applications that rely on middleware for authorization and could expose sensitive data to unauthorized users.

Technologies: [Vercel Next.js](https://junglewise.ai/threats/technologies/next-js). Vendors: [Vercel](https://junglewise.ai/threats/vendors/vercel).

## Quick answers

**Is CVE-2026-45109 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-45109 being exploited in the wild.

**How severe is CVE-2026-45109?** High severity, with a CVSS score of 7.5, published 13 May 2026.

**Which products and versions are affected?** Vercel Next.js >= 15.2.0, < 15.5.18; >= 16.0.0, < 16.2.6, >=15.2.0 <15.5.18, >=16.0.0 <16.2.6.

**Is there a fix for CVE-2026-45109?** A patch was published on 2026-05-07: Fix released in versions 15.5.18 and 16.2.6 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-45109 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-45109?** Check whether you run Vercel Next.js at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

This vulnerability is a follow-up to CVE-2026-44575 (GHSA-267c-6grr-h53f), an authentication bypass affecting Next.js App Router. The root cause is that middleware matchers do not properly handle transport-specific route variants (.rsc and segment-prefetch URLs) when Turbopack is used as the build tool. An unauthenticated attacker can craft specially crafted requests to these variant routes to bypass authorization checks that would normally apply to the standard page URLs. The vulnerability requires network access but no authentication or user interaction. The fix ensures App Router transport variants are consistently matched by middleware rules. Patches are available in versions 15.5.18 and 16.2.6.

## Affected products

- Vercel Next.js >=15.2.0 <15.5.18, >=16.0.0 <16.2.6

## Identifiers

- CVE-2026-45109
- GHSA-26hh-7cqf-hhc6

## Timeline

- 2026-05-07: disclosed: Vulnerability publicly disclosed
- 2026-05-07: patched: Fix released in versions 15.5.18 and 16.2.6

## References

- [https://github.com/vercel/next.js/security/advisories/GHSA-267c-6grr-h53f](https://github.com/vercel/next.js/security/advisories/GHSA-267c-6grr-h53f)
- [https://github.com/vercel/next.js/security/advisories/GHSA-26hh-7cqf-hhc6](https://github.com/vercel/next.js/security/advisories/GHSA-26hh-7cqf-hhc6)
- [https://github.com/vercel/next.js](https://github.com/vercel/next.js)
- [https://github.com/vercel/next.js/releases/tag/v15.5.18](https://github.com/vercel/next.js/releases/tag/v15.5.18)
- [https://github.com/vercel/next.js/releases/tag/v16.2.6](https://github.com/vercel/next.js/releases/tag/v16.2.6)

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