CVE-2025-59899 identifies a persistent Cross-Site Scripting (XSS) vulnerability in Flexense Sync Breeze Enterprise Server version 10.4.18 and Disk Pulse Enterprise v10.4.18. The vulnerability is classified under CWE-79, indicating improper neutralization of input during web page generation. Specifically, the issue exists in the '/server_options?sid=' endpoint where several parameters ('tasks_logs_dir', 'errors_logs_dir', 'error_notifications_address', 'status_notifications_address', and 'status_reports_address') do not properly sanitize user-supplied input. This allows an attacker with authenticated access to inject malicious JavaScript code that is stored persistently and executed in the context of other authenticated users who access the affected interface. The CVSS 4.0 score is 5.1 (medium severity), reflecting that the attack vector is network-based with low attack complexity, no privileges required beyond authentication, and requires user interaction. The vulnerability primarily threatens confidentiality by enabling session hijacking or theft of sensitive information from authenticated sessions. There is no indication of impact on system integrity or availability. No public exploits have been reported to date, but the presence of persistent XSS in an enterprise server product used for file synchronization and monitoring presents a significant risk if exploited. The vulnerability was reserved in September 2025 and published in January 2026. The lack of available patches at the time of reporting suggests that organizations must implement interim mitigations. The vulnerability is particularly relevant for environments where multiple users access the Sync Breeze Enterprise Server web interface, as the persistent nature of the XSS can affect multiple users over time.

For European organizations, this vulnerability poses a risk of session hijacking and unauthorized access to sensitive information through the exploitation of persistent XSS. Organizations using Sync Breeze Enterprise Server for file synchronization and monitoring could see compromised user sessions, leading to potential data leakage or unauthorized actions performed under the guise of legitimate users. While the vulnerability does not directly impact system availability or integrity, the confidentiality breach can have downstream effects such as unauthorized data access or lateral movement within networks. Sectors such as finance, healthcare, and critical infrastructure that rely on secure file management and monitoring are particularly at risk. The requirement for authentication limits the attack surface to internal or trusted users, but social engineering or credential compromise could enable attackers to exploit this vulnerability. The absence of known exploits in the wild reduces immediate risk but does not eliminate the threat, especially as attackers often develop exploits post-disclosure. European organizations must consider the regulatory implications of data breaches resulting from such vulnerabilities, including GDPR compliance and potential fines.

1. Apply patches or updates from Flexense as soon as they become available to address the input validation flaws. 2. Until patches are released, restrict access to the Sync Breeze Enterprise Server web interface to trusted users and networks only, using network segmentation and firewall rules. 3. Implement Web Application Firewall (WAF) rules to detect and block suspicious input patterns targeting the vulnerable parameters. 4. Conduct input validation and sanitization on the server side for all user-supplied data, especially in the affected parameters, to neutralize malicious scripts. 5. Educate authenticated users about the risks of clicking on suspicious links or content within the application to reduce the chance of exploitation. 6. Monitor logs and user activity for unusual behavior indicative of XSS exploitation or session hijacking attempts. 7. Consider disabling or limiting the use of affected parameters if they are not essential to operations. 8. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts within the web application context. 9. Regularly review and audit web application security controls and user privileges to minimize exposure.