CVE-2025-51479 is an authorization bypass vulnerability identified in the Onyx Enterprise Edition 0.27.0, specifically within the update_user_group function. This vulnerability allows remote authenticated attackers to modify arbitrary user groups by sending crafted PATCH requests to the /api/manage/admin/user-group/id endpoint. The flaw bypasses the intended curator-group assignment checks, which are presumably designed to restrict which user groups can be assigned or modified by certain roles. By exploiting this vulnerability, an attacker with valid authentication credentials can escalate privileges or alter user group memberships beyond their authorized scope. This could lead to unauthorized access to sensitive resources or administrative functions within the Onyx Enterprise Edition environment. The vulnerability does not require unauthenticated access but leverages insufficient authorization controls post-authentication. No CVSS score has been assigned yet, and there are no known exploits in the wild at this time. The affected version is 0.27.0, and no patch links are currently available, indicating that remediation may still be pending or in development.

For European organizations using Onyx Enterprise Edition 0.27.0, this vulnerability poses a significant risk to internal security controls. Unauthorized modification of user groups can lead to privilege escalation, allowing attackers to gain administrative rights or access to sensitive data and systems. This can compromise confidentiality, integrity, and availability of organizational data. Particularly in sectors with strict regulatory requirements such as finance, healthcare, and government, unauthorized access could result in data breaches, regulatory non-compliance, and reputational damage. Additionally, attackers could use this vulnerability to create persistent backdoors by assigning themselves or malicious users to privileged groups. The impact is amplified in environments where Onyx Enterprise Edition is integrated with critical infrastructure or sensitive workflows. Since exploitation requires authentication, the threat is more relevant in scenarios where attackers have obtained valid credentials through phishing, credential stuffing, or insider threats.

Organizations should immediately review and restrict access to the /api/manage/admin/user-group/id endpoint to trusted administrators only, implementing strict role-based access controls (RBAC). Monitoring and logging of all user group modification requests should be enhanced to detect anomalous or unauthorized changes. Multi-factor authentication (MFA) should be enforced to reduce the risk of credential compromise. Until an official patch is released, consider implementing web application firewall (WAF) rules to detect and block suspicious PATCH requests targeting user group modifications. Conduct thorough audits of user group memberships to identify and remediate any unauthorized changes. Additionally, organizations should engage with Onyx support or vendor channels to obtain timely patches or workarounds. Regular security training to reduce credential theft risks and prompt incident response plans are also recommended.