CVE-2025-46345 is an authentication bypass vulnerability identified in the Auth0 Account Link Extension, specifically affecting versions from 2.3.4 up to but not including 2.6.7. This extension is designed to facilitate the linking of multiple user accounts within the Auth0 identity platform. The core issue arises because these affected versions fail to verify the signature of the JSON Web Token (JWT) provided during the account linking process. JWTs are commonly used for securely transmitting information between parties as a JSON object, and their signature verification is critical to ensure the token's authenticity and integrity. The absence of signature verification allows an attacker to craft a forged JWT, effectively spoofing authentication credentials. This flaw enables unauthorized users to bypass authentication controls and gain access to user information without proper authorization. The vulnerability is classified under CWE-290, which pertains to improper authentication mechanisms. The vulnerability has been addressed in versions 2.6.7, 2.7.0, and 3.0.0 of the extension, with the recommendation to upgrade to version 3.0.0 or later to mitigate the risk. The CVSS v4.0 base score is 6.9, indicating a medium severity level. The vector string (AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N) highlights that the vulnerability is remotely exploitable over the network without requiring authentication or user interaction, and it primarily impacts confidentiality with limited scope. No known exploits have been reported in the wild as of the publication date (May 1, 2025).

For European organizations utilizing the Auth0 Account Link Extension within the affected version range, this vulnerability poses a significant risk to the confidentiality of user data. Attackers exploiting this flaw can impersonate legitimate users by supplying forged JWTs, potentially accessing sensitive personal or corporate information linked to user accounts. This can lead to unauthorized data disclosure, privacy violations, and potential regulatory non-compliance under frameworks such as GDPR. The integrity and availability of systems are less directly impacted; however, unauthorized access can facilitate further malicious activities, including lateral movement or privilege escalation within the affected environment. Organizations relying on Auth0 for identity and access management, especially those integrating multiple user accounts or services via the Account Link Extension, are at heightened risk. The ease of exploitation (no authentication or user interaction required) increases the threat level, particularly in environments exposed to the internet. The absence of known active exploits provides a window for remediation but should not reduce the urgency of patching. Given the widespread adoption of Auth0 in European enterprises, especially in sectors like finance, healthcare, and technology, the potential impact is substantial if left unaddressed.

1. Immediate Upgrade: Organizations should prioritize upgrading the Auth0 Account Link Extension to version 3.0.0 or later, where the signature verification flaw has been corrected. 2. Token Validation Auditing: Conduct thorough audits of JWT handling processes to ensure all tokens are properly validated, including signature verification, issuer, audience, and expiration claims. 3. Implement Defense-in-Depth: Complement Auth0's controls with additional monitoring and anomaly detection for unusual account linking activities or suspicious token usage patterns. 4. Restrict Exposure: Limit the exposure of the account linking endpoints to trusted networks or implement strict network access controls and Web Application Firewalls (WAFs) to detect and block malformed tokens. 5. Incident Response Preparedness: Develop and test incident response plans specific to identity compromise scenarios, including rapid revocation of tokens and user session invalidation. 6. Vendor Communication: Maintain active communication with Auth0 for updates and advisories related to this extension and related components. 7. User Awareness: Educate users and administrators about the risks of forged tokens and encourage vigilance for unusual account behaviors. These steps go beyond generic patching by emphasizing validation hygiene, network controls, and operational readiness.