CVE-2026-42280 Overview
CVE-2026-42280 is an improper authorization vulnerability [CWE-863] in Auth0.js, the client-side JavaScript library for Auth0. Versions 8.11.0 through 9.32.0 are affected. Under specific preconditions, the Auth0.js SDK returns user profile information using a valid access token when a specifically crafted invalid ID token is provided. The flaw allows an authenticated attacker to bypass token validation logic and obtain profile data that should be rejected. Auth0 fixed the issue in version 10.0.0.
Critical Impact
An attacker with a valid access token can supply a crafted invalid ID token and still receive user profile information, breaking the integrity of identity validation in client-side authentication flows.
Affected Products
- Auth0.js SDK versions 8.11.0 through 9.32.0
- Web applications embedding vulnerable Auth0.js builds
- Single-page applications relying on Auth0.js for ID token validation
Discovery Timeline
- 2026-05-27 - CVE-2026-42280 published to the National Vulnerability Database
- 2026-05-27 - Last updated in NVD database
Technical Details for CVE-2026-42280
Vulnerability Analysis
Auth0.js is a browser-side library that handles OAuth 2.0 and OpenID Connect flows for Auth0 tenants. The library exchanges credentials for access tokens and ID tokens, then validates the ID token before exposing user identity claims to the application.
In affected versions, the SDK does not consistently reject responses when the ID token fails validation. Under specific preconditions, the library still returns the user profile derived from the associated access token. The application therefore receives identity information bound to a token that should have been rejected.
The issue is classified as [CWE-863] Incorrect Authorization. It impacts confidentiality of user profile data and integrity of identity assertions consumed by the client. The fix in 10.0.0 corrects the validation flow so profile responses depend on successful ID token verification.
Root Cause
The root cause is an authorization gap between access token validity and ID token validity. The SDK conflates the two trust signals. When the ID token is malformed or fails verification but a valid access token is present, the profile retrieval path proceeds rather than aborting.
Attack Vector
The attack vector is network-based with low complexity and requires low privileges. An attacker who already controls a valid access token in a multi-tenant or shared authentication context crafts an invalid ID token. The vulnerable Auth0.js client accepts the response and exposes profile information that should be gated by ID token validation. See the GitHub Security Advisory GHSA-8qjv-jj2q-x832 for vendor-confirmed technical details.
Detection Methods for CVE-2026-42280
Indicators of Compromise
- Application logs showing successful getUser or profile retrievals correlated with ID tokens that fail server-side re-validation.
- Browser telemetry reporting Auth0.js bundle versions in the range 8.11.0 to 9.32.0.
- Authentication events where the id_token signature, aud, iss, or nonce claims do not match expected tenant values but the session proceeds.
Detection Strategies
- Inventory all front-end bundles and package-lock.json files for auth0-js versions below 10.0.0.
- Re-validate ID tokens server-side on every profile-bound request and alert when validation fails but a profile response was issued client-side.
- Compare access token subject (sub) claims against ID token sub claims and flag mismatches.
Monitoring Recommendations
- Forward Auth0 tenant logs to a centralized analytics platform and build queries for failed ID token validations paired with successful profile reads.
- Monitor build pipelines to block deployments that pin vulnerable Auth0.js versions.
- Track anomalous spikes in userinfo endpoint requests originating from a single access token.
How to Mitigate CVE-2026-42280
Immediate Actions Required
- Upgrade Auth0.js to version 10.0.0 or later in all production and staging applications.
- Audit dependency manifests for transitive references to vulnerable auth0-js versions and rebuild affected bundles.
- Rotate any user sessions or tokens issued during the window the vulnerable SDK was in use if exposure is suspected.
Patch Information
Auth0 fixed CVE-2026-42280 in Auth0.js 10.0.0. The patched release corrects ID token validation so user profile information is no longer returned when validation fails. Refer to the GitHub Security Advisory GHSA-8qjv-jj2q-x832 for the upstream advisory and release notes.
Workarounds
- Perform ID token validation on a trusted backend before returning profile data to the client, rather than relying solely on Auth0.js client-side checks.
- Enforce strict nonce, aud, and iss checks against tenant configuration on the server.
- Restrict access token scopes so that compromise of a single token cannot retrieve sensitive profile attributes.
# Upgrade Auth0.js to the patched release
npm install auth0-js@^10.0.0
npm ls auth0-js
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
