CVE-2025-59901 is a Cross-Site Request Forgery (CSRF) vulnerability classified under CWE-352, affecting Flexense Sync Breeze Enterprise Server version 10.4.18. The vulnerability exists in the '/monitor_directory?sid=' endpoint, where the 'monitor_directory' parameter sent via POST requests is insufficiently validated. This flaw allows an attacker to craft malicious requests that, when executed by an authenticated user, can perform unauthorized actions on their behalf. The vulnerability is reflected and requires user interaction, as the attacker must trick the user into submitting the malicious request. The CVSS 4.0 vector indicates the attack is network-based (AV:N), with low complexity (AC:L), no privileges required (PR:L), but user interaction is necessary (UI:A). The impact on confidentiality, integrity, and availability is high (VC:H, VI:H, VA:H), meaning an attacker could steal sensitive session data, manipulate server state, or disrupt service availability. Although no public exploits or patches are currently available, the vulnerability poses a significant risk to organizations relying on this software for enterprise file synchronization and monitoring. The vulnerability was reserved in September 2025 and published in January 2026, with INCIBE as the assigner. Given the nature of CSRF attacks, the threat is particularly relevant in environments where users have elevated privileges or access to sensitive data through the Sync Breeze Enterprise Server interface.

For European organizations, exploitation of CVE-2025-59901 could lead to unauthorized actions performed under the context of authenticated users, including data theft, unauthorized configuration changes, or service disruption. This is especially critical for enterprises that use Sync Breeze Enterprise Server for file synchronization and monitoring, as attackers could manipulate monitored directories or exfiltrate sensitive information. The high impact on confidentiality, integrity, and availability means that data breaches, operational downtime, or compliance violations could occur, potentially resulting in financial loss and reputational damage. Organizations in sectors such as finance, healthcare, and critical infrastructure are particularly at risk due to the sensitivity of the data and the regulatory environment in Europe (e.g., GDPR). The lack of available patches increases the urgency for proactive mitigation. Additionally, the requirement for user interaction means that phishing or social engineering campaigns could be leveraged to exploit this vulnerability, increasing the attack surface.

European organizations should implement several specific measures to mitigate this vulnerability beyond generic advice: 1) Employ strict Content Security Policy (CSP) headers to limit the execution of malicious scripts and reduce the risk of CSRF exploitation. 2) Use anti-CSRF tokens in all state-changing POST requests, ensuring that the server validates these tokens before processing requests. 3) Restrict the use of the vulnerable endpoint '/monitor_directory?sid=' to trusted internal networks or VPNs to reduce exposure. 4) Implement multi-factor authentication (MFA) to reduce the risk of session hijacking and unauthorized access. 5) Educate users about phishing and social engineering tactics that could be used to trigger CSRF attacks. 6) Monitor server logs for unusual POST requests to the vulnerable endpoint, enabling early detection of exploitation attempts. 7) Coordinate with Flexense for timely patch deployment once available and consider temporary workarounds such as disabling the vulnerable feature if feasible. 8) Employ web application firewalls (WAF) with custom rules to detect and block suspicious requests targeting the vulnerable parameter. These targeted actions will help reduce the risk while awaiting official patches.