CVE-2022-39346 is a medium-severity vulnerability affecting Nextcloud Server, an open-source personal cloud server widely used for file sharing and collaboration. The vulnerability arises from improper input validation related to user display names. Specifically, affected versions of Nextcloud Server do not properly limit the length or content of user display names. This lack of validation can be exploited by a malicious user to submit excessively large or malformed display names, which in turn overloads the underlying database. The consequence is uncontrolled resource consumption, leading to a denial of service (DoS) condition where legitimate users may be unable to access the service or experience significant performance degradation. The affected versions include all releases prior to 22.2.10, versions from 23.0.0 up to but not including 23.0.7, and versions from 24.0.0 up to but not including 24.0.3. The vulnerability is categorized under CWE-400 (Uncontrolled Resource Consumption) and CWE-20 (Improper Input Validation). There are no known workarounds, and remediation requires upgrading to fixed versions 22.2.10, 23.0.7, or 24.0.3. No public exploits have been reported in the wild to date. The vulnerability does not require authentication or user interaction beyond submitting a crafted display name, which may be possible if user registration or profile editing is allowed. The attack vector is thus relatively straightforward for an authenticated user, but the impact is limited to resource exhaustion and denial of service rather than data breach or privilege escalation.

For European organizations using Nextcloud Server, this vulnerability poses a risk of service disruption due to denial of service attacks. Organizations relying on Nextcloud for critical collaboration, document sharing, or internal communication may experience downtime or degraded performance, impacting productivity and operational continuity. Since Nextcloud is popular among public sector entities, educational institutions, and private enterprises across Europe, the disruption could affect sensitive workflows and data availability. Although the vulnerability does not directly compromise confidentiality or integrity, the denial of service could indirectly impact business operations and user trust. Additionally, organizations with limited IT resources or those slow to apply patches may be more vulnerable to exploitation. The lack of known exploits reduces immediate risk, but the simplicity of the attack vector means that threat actors could develop exploits if motivated. The impact is primarily on availability, with potential cascading effects on dependent services and user access.

The primary mitigation is to upgrade Nextcloud Server to one of the patched versions: 22.2.10, 23.0.7, or 24.0.3. Organizations should prioritize patching in environments where user registration or profile editing is enabled, especially if exposed to untrusted users. Beyond upgrading, administrators should implement input validation controls at the application or web server level to limit the length and character set of user display names, reducing the risk of resource exhaustion. Monitoring database performance and resource utilization can help detect anomalous activity indicative of exploitation attempts. Rate limiting or throttling user profile updates may also mitigate attack impact. In environments where immediate patching is not feasible, restricting user registration or profile editing to trusted users can reduce exposure. Regular backups and incident response plans should be updated to address potential denial of service scenarios. Finally, organizations should stay informed on Nextcloud advisories and community reports for any emerging exploit developments.