CVE-2025-66296 is a vulnerability classified under CWE-266 (Incorrect Privilege Assignment) affecting the Grav CMS, a file-based web platform widely used for content management. The flaw exists in the Admin plugin versions before 1.8.0-beta.27, where the system fails to enforce uniqueness of usernames during user creation. An attacker who has the permission to create users but does not have full administrative rights can exploit this by creating a new user account with the exact username of an existing administrator. Since the system does not prevent duplicate usernames, the attacker can set a new password and email address for this duplicate account. Consequently, the attacker can log in as the administrator, effectively escalating their privileges from a limited user-manager role to full administrator access. This bypasses normal authentication and authorization controls, compromising the confidentiality, integrity, and availability of the Grav installation. The vulnerability is remotely exploitable over the network without user interaction and requires only low privileges (create user permission). The CVSS 3.1 base score is 8.8, reflecting high impact and ease of exploitation. Although no public exploits are known yet, the vulnerability poses a significant risk to affected systems. The issue was addressed and fixed in Grav version 1.8.0-beta.27 by enforcing username uniqueness validation during user creation.

For European organizations using Grav CMS versions prior to 1.8.0-beta.27, this vulnerability could lead to full compromise of their web platforms. Attackers can gain administrative access, allowing them to modify website content, inject malicious code, steal sensitive data, or disrupt services. This can result in reputational damage, regulatory non-compliance (e.g., GDPR violations due to data breaches), and financial losses. The ability to escalate privileges without user interaction and remotely increases the attack surface significantly. Organizations relying on Grav for public-facing websites or intranet portals are particularly at risk. The impact extends to any sector using Grav, including government, education, media, and small-to-medium enterprises across Europe. Given the high CVSS score and the critical nature of administrative access, the threat is severe and demands immediate attention.

1. Upgrade all Grav CMS installations to version 1.8.0-beta.27 or later immediately to apply the official fix that enforces username uniqueness validation. 2. Audit existing user accounts for duplicate usernames and remove or rename duplicates to prevent exploitation. 3. Restrict 'create user' permissions strictly to trusted administrators only, minimizing the number of users who can create accounts. 4. Implement multi-factor authentication (MFA) for all administrator accounts to add an additional security layer. 5. Monitor logs for suspicious user creation activities, especially attempts to create accounts with existing administrator usernames. 6. Conduct regular security assessments and penetration tests focusing on user management functionalities. 7. Educate administrators and users about the risks of privilege escalation and the importance of strong access controls. 8. Consider deploying web application firewalls (WAFs) with custom rules to detect and block anomalous user creation requests targeting this vulnerability.