High

Reflected XSS when using flashMessages or languageDictionary

Disclosed: 04.06.2021
Updated: 11.10.2026 10:22

Overview

Versions before and including 11.30.0 are vulnerable to reflected XSS. An attacker can execute arbitrary code when the library's

flashMessage feature is utilized and user input or data from URL parameters is incorporated into the flashMessage.
languageDictionary feature is utilized and user input or data from URL parameters is incorporated into the languageDictionary.

Am I affected?

You are affected by this vulnerability if you are using auth0-lock version 11.30.0 or lower and all of the following conditions apply:

You are utilizing flashMessage feature.
User input or data from URL parameters is incorporated into the flashMessage.

An example of a vulnerable snippet where query parameters are used to populate the text property of a flashMessage.

var params = new URLSearchParams(location.search);
var errorMessage = params.get('error__message');
var showParams = {};

if (!!errorMessage === true) {
  showParams.flashMessage = {
    type: 'error',
    text: 'We were unable to log you in. ' + errorMessage,
  };
}

lock.show(showParams);

You are utilizing languageDictionary feature.
User input or data from URL parameters is used in languageDictionary properties.

An example of a vulnerable snippet where query parameters are used to populate the socialLoginInstructions property of a languageDictionary.

var params = new URLSearchParams(location.search);
var instruction = params.get('instruction');

var options = {
  languageDictionary: {
    emailInputPlaceholder: "something@youremail.com",
    title: "title",
    socialLoginInstructions: instruction
  },
};

var lock = new Auth0LockPasswordless(
    CLIENT_ID,
    DOMAIN,
    options
);

lock.show()

How to fix that?

Upgrade to version 11.30.1.

Will this update impact my users?

The fix uses DOMPurify to sanitise the flashMessage and languageDictionary inputs. If you are including inline JavaScript in these fields, like script tags or onclick attributes, these will be removed.

Affected software

Click a technology to see all vulnerabilities affecting it.

Platform	Package	Vulnerable versions	Fixed in
npm package	auth0-lock	< 11.30.1	11.30.1

References

CVSS score 8.1/10

CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE): CWE-79
Platform: npm
Package: auth0-lock
Disclosed: 04.06.2021
Updated: 11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-jr3j-whm4-9wwm - CC BY 4.0

Vulnerability history: auth0-lock

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

Total entries: 4
First → latest: 01.2020 05.2022
Without a fix: 0
Exploited in attacks: 0

Severity breakdown

High 1
Medium 2
Low 1

Disclosures per year

2020: 2
2021: 1
2022: 1
2023: 0
2024: 0
2025: 0
2026: 0

24.05.2022

Cross-site Scripting in Auth0 Lock

Medium · 6.1 CVE-2022-29172 < 11.33.0 11.33.0
04.06.2021

Reflected XSS when using flashMessages or languageDictionary this entry

High · 8.1 CVE-2021-32641 < 11.30.1 11.30.1
19.08.2020

DOM-based XSS in auth0-lock

Low · 6.4 CVE-2020-15119 < 11.26.3 11.26.3
31.01.2020

auth0-lock vulnerable to XSS via unsanitized placeholder property

Medium · 6.1 CVE-2019-20174 < 11.21.0 11.21.0

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