CVE-2021-32702: Reflected XSS from the callback handler's error query parameter

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-06-25 · updated 2026-06-17
Weakness: CWE-79

Description

The Auth0 Next.js SDK is a library for implementing user authentication in Next.js applications. Versions before and including `1.4.1` are vulnerable to reflected XSS. An attacker can execute arbitrary code by providing an XSS payload in the `error` query parameter which is then processed by the callback handler as an error message. You are affected by this vulnerability if you are using `@auth0/nextjs-auth0` version `1.4.1` or lower **unless** you are using custom error handling that does not return the error message in an HTML response. Upgrade to version `1.4.1` to resolve. The fix adds basic HTML escaping to the error message and it should not impact your users.

Affected products

auth0 nextjs-auth0: before 1.4.2 — fixed in 1.4.2

How to fix

Upgrade to a fixed version: auth0 nextjs-auth0 1.4.2. Check the vendor advisory for mitigations.

References

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