Summary
auth0-lock vulnerable to XSS via unsanitized placeholder property
Overview
Auth0 Lock version 11.20.4 and earlier did not properly sanitize the generated HTML code. Customers using the additionalSignUpFields customization option to add a checkbox to the sign-up dialog that are passing a placeholder property obtained from an untrusted source (e.g. a query parameter) could allow cross-site scripting (XSS) on their signup pages.
Am I affected?
You are affected by this vulnerability if all of the following conditions apply:
- You are using Auth0 Lock version 11.20.4 or earlier.
- You pass
additionalSignUpFieldsas options when initializing Lock which includes a field of typecheckboxwhoseplaceholdervalue is obtained from an untrusted source.
An example of a vulnerable snippet is the following where the placeholder value is partially user-controlled by the name query parameter:
<script>
var params = new URLSearchParams(window.location.search);
var options = {
auth: {
redirectUrl: 'http://localhost:12345/callback',
responseType: 'code',
params: {
scope: 'openid email',
},
},
additionalSignUpFields: [{
name: 'agree',
type: 'checkbox',
placeholder: "I agree to Terms and Conditions for " + params.get('name'),
}],
};
var lock = new Auth0Lock('<CLIENT_ID>', '<TENANT_NAME>.auth0.com', options);
lock.show({
allowShowPassword: true,
initialScreen: 'signUp',
});
</script>
How to fix that?
Developers using Auth0’s signin solution Lock need to upgrade to version 11.21.0 or later. Version 11.21.0 introduces two changes:
- The existing
placeholderproperty is now treated as plain text to mitigate the problem. - A new
placeholderHTMLproperty is introduced that indicates the level of control it provides and that it should be only supplied from trusted sources.
Will this update impact my users?
This fix patches the Auth0 Lock widget and may require changes in application code, but it will not impact your users, their current state, or any existing sessions.
Developers using the placeholder property with HTML content from a trusted source should start using the placeholderHTML property to continue providing the same user experience.
Impact
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
CVE-2019-20174 has a CVSS score of 6.1 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (11.21.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2019-20174? CVE-2019-20174 is a medium-severity cross-site scripting (XSS) vulnerability in auth0-lock (npm), affecting versions < 11.21.0. It is fixed in 11.21.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- How severe is CVE-2019-20174? CVE-2019-20174 has a CVSS score of 6.1 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of auth0-lock are affected by CVE-2019-20174? auth0-lock (npm) versions < 11.21.0 is affected.
- Is there a fix for CVE-2019-20174? Yes. CVE-2019-20174 is fixed in 11.21.0. Upgrade to this version or later.
- Is CVE-2019-20174 exploitable, and should I be worried? Whether CVE-2019-20174 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2019-20174 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2019-20174? Upgrade
auth0-lockto 11.21.0 or later.