Auth bypass in Auth0 Nextjs-Auth0
CVE-2026-40155
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.
Vulnerability class: Race Condition
EPSS: 0.002 (12.0th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:L/A:N.
Affected products
- Auth0 Nextjs-auth0 — versions >= 4.12.0, < 4.18.0
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
- security-advisories@github.com (Product, x_refsource_MISC, Release Notes)
Frequently asked questions
- What is CVE-2026-40155?
- CVE-2026-40155 is a medium-severity vulnerability in Auth0 Nextjs-Auth0, classified under Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). CVSS score: 5.4/10. Published 2026-04-17.
- How severe is CVE-2026-40155?
- Medium severity. CVSS v3 base score is 5.4 out of 10.