CVE-2019-20174 in Lock
Summary
by MITRE
Auth0 Lock before 11.21.0 allows XSS when additionalSignUpFields is used with an untrusted placeholder.
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Analysis
by VulDB Data Team • 03/28/2024
The vulnerability identified as CVE-2019-20174 affects Auth0 Lock versions prior to 11.21.0 and represents a cross-site scripting vulnerability that arises from improper input validation when processing additional sign up fields. This flaw specifically manifests when the additionalSignUpFields configuration parameter is utilized with untrusted placeholder values, creating a pathway for malicious actors to inject arbitrary JavaScript code into the authentication flow.
The technical implementation of this vulnerability stems from the insecure handling of user-provided data within the Auth0 Lock library's form field rendering mechanism. When developers configure additional sign up fields using the additionalSignUpFields parameter, the system processes placeholder values without adequate sanitization or encoding. This oversight allows attackers to craft malicious placeholder content that gets directly embedded into the HTML output, bypassing standard security controls that would normally prevent such injections. The vulnerability falls under CWE-79 - Cross-site Scripting and aligns with ATT&CK technique T1203 - Exploitation for Client Execution, as it enables remote code execution within the context of the victim's browser session.
The operational impact of this vulnerability extends beyond simple script injection, as it can enable attackers to perform session hijacking, data exfiltration, and credential theft. An attacker who successfully exploits this vulnerability could steal authentication tokens, access sensitive user data, or redirect users to malicious sites. The vulnerability is particularly concerning because it affects the authentication layer itself, potentially compromising the entire security posture of applications relying on Auth0 Lock for user registration and login processes. The attack vector requires minimal privileges as it only necessitates the ability to influence the placeholder value used in the additionalSignUpFields configuration, making it accessible to attackers who can manipulate application settings or configuration parameters.
Mitigation strategies for CVE-2019-20174 primarily involve upgrading to Auth0 Lock version 11.21.0 or later, which implements proper input sanitization and encoding for placeholder values in additional sign up fields. Organizations should also implement strict input validation policies for any user-provided configuration data, particularly within authentication frameworks. Additional defensive measures include implementing content security policies that restrict script execution, using parameterized inputs where possible, and conducting regular security assessments of authentication components. Security teams should also monitor for any custom implementations that might bypass the standard Lock library functionality and ensure proper sanitization of all dynamic content within authentication forms. The vulnerability demonstrates the critical importance of input validation in authentication systems and highlights how seemingly innocuous configuration parameters can become attack vectors when proper security controls are not implemented.