# CVE-2026-40155: Auth0 Next.js SDK has Improper Proxy Cache Lookup

> Simultaneous requests with DPoP enabled may cause improper proxy cache lookups, potentially bypassing authentication checks in Next.js applications.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 17 Apr 2026
- **Updated:** 20 Apr 2026
- **Also known as:** GHSA-xq8m-7c5p-c2r6

## What is CVE-2026-40155?

CVE-2026-40155 is a medium-severity vulnerability in nextjs-auth0, published on 17 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

The Auth0 Next.js SDK is a library for implementing user authentication in Next.js applications. In versions 4.12.0 through 4.17.1, simultaneous requests that trigger a nonce retry may cause the proxy cache fetcher to perform improper lookups for the token request results. Users are affected if their project uses both the vulnerable versions and the proxy handler /me/* and /my-org/* with DPoP enabled. This issue has been fixed in version 4.18.0.

Weakness: CWE-863 (Incorrect Authorization), CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-40155?

2 open source packages ship an affected version, including @auth0/nextjs-auth0. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@auth0/nextjs-auth0` | npm | From 4.12.0 | 4.18.0 |
| `@auth0/nextjs-auth0` | npm | From 4.12.0 | 4.18.0 |

Products: Auth0 Nextjs-Auth0.

## How do I fix CVE-2026-40155?

Upgrade @auth0/nextjs-auth0 to 4.18.0 or later.

## Is CVE-2026-40155 being exploited?

There is no known exploitation of CVE-2026-40155 in the wild and no public exploit code.

## Other vulnerabilities in nextjs-auth0

- [CVE-2021-32702](https://insights.sbomify.com/CVE-2021-32702/): Reflected XSS from the callback handler's error query parameter (high 8.0)
- [CVE-2021-43812](https://insights.sbomify.com/CVE-2021-43812/): Open redirect in nextjs-auth0 (medium 6.4)
- [CVE-2025-67716](https://insights.sbomify.com/CVE-2025-67716/): Auth0 Next.js SDK has Improper Validation of Query Parameters (medium 5.7)
- [CVE-2025-67490](https://insights.sbomify.com/CVE-2025-67490/): Auth0 Next.js SDK has Improper Request Caching Lookup (medium 5.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40155 and fix it if it is affected.

What it is: CVE-2026-40155 is a medium-severity vulnerability in nextjs-auth0, published on 17 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-40155 in the wild and no public exploit code.

Affected packages and fixed versions:
- @auth0/nextjs-auth0 (npm): affected from 4.12.0; fixed in 4.18.0
- @auth0/nextjs-auth0 (npm): affected from 4.12.0; fixed in 4.18.0

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-2026-40155/ (Markdown: https://insights.sbomify.com/CVE-2026-40155/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40155
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40155
- OSV: https://osv.dev/vulnerability/CVE-2026-40155

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40155/
Summaries are generated and may contain mistakes; the official description above is the record.