CVE-2018-6873 in Auth0
Summary
by MITRE
The Auth0 authentication service before 2017-10-15 allows privilege escalation because the JWT audience is not validated.
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Analysis
by VulDB Data Team • 01/22/2020
The vulnerability identified as CVE-2018-6873 represents a critical security flaw in the Auth0 authentication service that existed prior to the October 15, 2017 release. This issue stems from the improper validation of JSON Web Token (JWT) audience claims within the authentication process, creating a significant privilege escalation vector that adversaries could exploit to gain unauthorized access to systems. The flaw specifically affects the service's ability to verify that tokens are intended for the correct recipient, allowing attackers to manipulate authentication flows and potentially elevate their privileges within the affected environment.
The technical root cause of this vulnerability lies in the absence of proper JWT audience validation mechanisms within the Auth0 service implementation. When authentication tokens are issued, they typically contain an audience claim that specifies which service or application the token is intended for. In the vulnerable version of Auth0, this validation step was omitted or inadequately implemented, allowing tokens issued for one application to be accepted by another application that should have been protected from such access. This weakness directly violates the fundamental security principle of least privilege and enables attackers to leverage valid authentication tokens in contexts for which they were never intended.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it creates opportunities for attackers to perform privilege escalation attacks that could lead to complete system compromise. An attacker who successfully exploits this vulnerability could potentially access administrative functions, modify user permissions, or gain access to sensitive data that should have been protected from their initial authentication scope. The implications are particularly severe in environments where Auth0 serves as a central authentication service for multiple applications, as a single compromised token could potentially provide access across multiple systems within the organization's infrastructure.
This vulnerability aligns with CWE-290 authentication bypass weakness and relates to the broader category of insecure token handling practices that have been documented in numerous security frameworks and standards. The flaw demonstrates the critical importance of proper token validation in modern authentication systems and highlights the risks associated with inadequate implementation of industry-standard security controls. Organizations implementing JWT-based authentication systems should consider this vulnerability as a prime example of how seemingly minor implementation gaps can create significant security risks. The remediation for this issue involves implementing proper audience validation for JWT tokens, ensuring that tokens are only accepted when their audience claim matches the intended recipient service. This fix aligns with the ATT&CK framework's privilege escalation techniques, specifically targeting the use of valid credentials in unauthorized contexts. Security teams should prioritize updating their Auth0 implementations to versions that properly validate JWT audience claims and implement comprehensive token validation processes to prevent similar vulnerabilities from being exploited in their environments.