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The vulnerability arises from flawed audience claim validation in the Auth0-PHP SDK’s JWT token verification process. Access tokens and ID tokens have distinct audience requirements: access tokens must specify the API identifier as the audience, while ID tokens use the client ID. Due to improper validation logic, the SDK fails to enforce strict audience matching for access tokens. It may only check for the presence of an audience claim without verifying it against the configured API audience. In some scenarios, the validation incorrectly falls back to client ID checks, allowing ID tokens to be accepted as valid access tokens. This confusion between token types enables attackers to present ID tokens, which are intended for authentication, to endpoints expecting access tokens for authorization. ID tokens lack the scopes and permissions embedded in access tokens, leading to unauthorized access. The flaw occurs during token decoding and validation, where the audience parameter is not properly validated against the expected service identifier. Attackers can exploit this by obtaining an ID token through standard OAuth flows and injecting it into API requests. The application then mistakenly grants access based on the ID token, bypassing intended security controls. This vulnerability affects Laravel applications integrating Auth0 for authentication and authorization, particularly those using the SDK to protect API routes. The improper validation can result in privilege escalation, data exposure, and unauthorized actions. The issue is rooted in the SDK’s token handling library, which does not differentiate between token types during audience verification. Fixing this requires ensuring that access tokens are validated exclusively against the API audience, not the client ID.
Platform: Auth0 Laravel SDK
Version: Before 7.20.0
Vulnerability: Improper Audience Validation
Severity: Moderate
Date: Dec 17 2025
Prediction: Patched Dec 17 2025
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Showing bash commands and codes related to the blog
Bash commands:
composer show auth0/laravel-auth0
composer update auth0/laravel-auth0
php artisan auth0:install
Codes:
if ($token->aud !== $api_audience) { throw new Exception(); }
$verifier = new JWTVerifier([‘valid_audiences’ => [$api_audience]]);
How Exploit:
Send ID tokens as access tokens to API endpoints. Bypass audience validation checks. Gain unauthorized access.
Protection from this CVE
Upgrade to version 7.20.0. Configure correct API audience. Validate token types strictly.
Impact:
Unauthorized API access. Potential data breaches. Privilege escalation risks.
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Sources:
Reported By: github.com
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