CVE-2019-20174 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in auth0-lock. 1 public exploit reference exists, so weaponization risk is real. A fix is available for auth0-lock — see the affected versions and patch details below.
auth0-lock vulnerable to XSS via unsanitized placeholder property
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-2019-20174 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 378,567 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-locknpmDescription
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | auth0-lock | all versions | 11.21.0npm install auth0-lock@11.21.0 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for auth0-lock, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update auth0-lock to 11.21.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-20174 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-2019-20174 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2019-20174. 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-2019-20174 in your dependencies?
O3 Security finds CVE-2019-20174 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.