CVE-2026-40155 is a medium-severity (CVSS 5.4) CWE-362 vulnerability in @auth0/nextjs-auth0. A fix is available for @auth0/nextjs-auth0 — see the affected versions and patch details below.
Auth0 Next.js SDK has Improper Proxy Cache Lookup
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-40155.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-40155 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@auth0/nextjs-auth0npmDescription
Description
In affected versions of the Next.js SDK, simultaneous requests that trigger a nonce retry may cause the proxy cache fetcher to perform improper lookups for the token request results.
Which Projects are Affected?
Users are affected if they meet all of the following preconditions:
- Applications using the auth0/nextjs-auth0 SDK, versions 4.12.0 to 4.17.0, and
- Applications using the proxy handler /me/* and /my-org/* with DPoP enabled.
Affected product and versions
Auth0/nextjs-auth0 v4.12.0 to 4.17.0
Resolution
Upgrade Auth0/nextjs-auth0 version to v4.18.0 or greater
Acknowledgements
Okta would like to thank Reynaldo Immanuel for their discovery and responsible disclosure.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @auth0/nextjs-auth0 | ≥ 4.12.0&&< 4.18.0 | 4.18.0npm install @auth0/nextjs-auth0@4.18.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @auth0/nextjs-auth0, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @auth0/nextjs-auth0 to 4.18.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40155 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-40155 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-40155. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-40155 in your dependencies?
O3 Security finds CVE-2026-40155 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.