CVE-2025-66552 is a vulnerability classified under CWE-778 (Insufficient Logging) affecting Nextcloud Server and Enterprise Server versions prior to 30.0.9 and 31.0.1. The root cause is incorrect path handling within the groupfolders feature, which causes the admin_audit application to fail to log all file and folder actions inside these groupfolders. This insufficient logging undermines the audit trail's completeness, which is critical for detecting unauthorized access or modifications. The vulnerability does not allow direct data compromise but impairs visibility into user actions, potentially enabling attackers or malicious insiders to perform activities without triggering alerts or logs. The CVSS v3.1 base score is 4.3 (medium), reflecting that the attack vector is network-based, requires low privileges, and does not need user interaction, but the impact is limited to availability of audit logs rather than confidentiality or integrity. No known exploits are reported in the wild as of publication. The issue is resolved by upgrading to Nextcloud Server versions 30.0.9, 31.0.1, or later, where path handling and logging have been corrected to ensure comprehensive audit coverage of groupfolder operations.

For European organizations, this vulnerability primarily impacts the ability to detect and respond to unauthorized or malicious activities within Nextcloud groupfolders. Since Nextcloud is widely used in Europe, including by government agencies, educational institutions, and enterprises for secure file sharing and collaboration, incomplete audit logs can hinder forensic investigations and compliance with data protection regulations such as GDPR. Attackers or insiders exploiting this flaw could perform unauthorized file operations without leaving a full audit trail, increasing the risk of data misuse or exfiltration going unnoticed. While the vulnerability does not directly compromise data confidentiality or integrity, the reduced visibility can delay incident detection and response, potentially amplifying damage. Organizations relying on Nextcloud for sensitive or regulated data should consider this a significant operational risk until patched.

1. Upgrade all affected Nextcloud Server and Enterprise Server instances to version 30.0.9, 31.0.1, or later immediately to ensure the logging issue is resolved. 2. Conduct a thorough review of existing audit logs for gaps or missing entries related to groupfolder activities prior to patching, and investigate any suspicious or unexplained file operations. 3. Enhance monitoring and alerting around groupfolder access and modifications using supplementary security tools or SIEM integrations to compensate for any residual logging limitations. 4. Implement strict access controls and least privilege principles on groupfolders to minimize the risk of unauthorized actions. 5. Regularly verify the integrity and completeness of audit logs as part of security audits and compliance checks. 6. Educate administrators and security teams about this vulnerability and the importance of audit log completeness for incident response.