Quick answers
- Is CVE-2026-40155 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-40155 being exploited in the wild.
- How severe is CVE-2026-40155?
- Medium severity, with a CVSS score of 5.4, published 21 April 2026.
- Which products and versions are affected?
- @auth0/nextjs-auth0 (npm) >= 4.12.0, <= 4.17.0, SEMVER:introduced=4.12.0,fixed=4.18.0.
- Is there a fix for CVE-2026-40155?
- Yes. @auth0/nextjs-auth0 (npm): upgrade to 4.18.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-40155 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-40155?
- Check whether you run @auth0/nextjs-auth0 (npm) 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.
How to fix
- @auth0/nextjs-auth0 (npm): upgrade to 4.18.0 or later
npm install @auth0/nextjs-auth0@4.18.0
Technical details
The vulnerability is a race condition (improper cache lookup) in the proxy cache handler of Auth0's Next.js SDK versions 4.12.0–4.17.0. When simultaneous requests trigger nonce retry logic with DPoP (Demonstrating Proof-of-Possession) enabled on the /me/* and /my-org/* proxy endpoints, the cache fetcher fails to properly isolate token lookup results, causing one user's cached authentication token to be served to another concurrent request. This requires the attacker to have low-level privileges and user interaction to trigger, but can expose confidential user data. The vulnerability is patched in version 4.18.0.
Affected products
- Auth0 Next.js SDK 4.12.0 to 4.17.0
Identifiers
- CVE-2026-40155
- GHSA-xq8m-7c5p-c2r6
Timeline
- 2026-04-21: disclosed: GHSA-xq8m-7c5p-c2r6 published
- 2026-04-21: patched: Fixed in version 4.18.0