CVE-2025-66689 is a path traversal vulnerability identified in Zen MCP Server versions before 9.8.2. The root cause is a flawed validation mechanism in the is_dangerous_path() function, which attempts to prevent unauthorized file access by blacklisting certain system directories. However, this function uses exact string matching rather than a more robust path normalization or canonicalization approach. As a result, attackers with valid credentials can circumvent these restrictions by specifying subdirectories within the blacklisted paths, effectively bypassing the blacklist and gaining access to arbitrary files on the server. This vulnerability is classified under CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and CWE-552 (Files or Directories Accessible to External Parties). The attack vector is network-based, requiring low attack complexity and only privileges of an authenticated user, with no need for user interaction. The impact is primarily on confidentiality, as attackers can read sensitive files, but it does not compromise system integrity or availability. No public exploits have been reported yet, but the vulnerability poses a moderate risk given the potential exposure of sensitive data. The CVSS v3.1 score is 6.5, reflecting these factors. Organizations using Zen MCP Server should verify their version and apply updates or mitigations promptly to prevent exploitation.

For European organizations, this vulnerability could lead to unauthorized disclosure of sensitive information stored on Zen MCP Server systems. This may include configuration files, credentials, or other critical data that could facilitate further attacks or data breaches. The requirement for authentication limits exposure to insiders or compromised accounts, but the ease of bypassing path restrictions increases the risk. Confidentiality breaches could affect compliance with GDPR and other data protection regulations, potentially resulting in legal and financial consequences. Critical sectors such as finance, healthcare, and government that rely on Zen MCP Server for management and control functions may face operational risks if sensitive data is exposed. Although integrity and availability are not directly impacted, the loss of confidentiality alone can have severe repercussions for trust and security posture. The absence of known exploits currently provides a window for remediation, but organizations should act swiftly to mitigate risk.

European organizations should immediately identify all instances of Zen MCP Server in their environment and verify the version in use. Upgrading to version 9.8.2 or later, where the vulnerability is fixed, is the most effective mitigation. If immediate patching is not feasible, organizations should implement strict access controls to limit authenticated user privileges to only those necessary, reducing the risk of exploitation. Monitoring and logging access to sensitive files can help detect suspicious activity indicative of exploitation attempts. Additionally, network segmentation can isolate Zen MCP Server instances from less trusted networks and users. Reviewing and hardening authentication mechanisms, including enforcing strong password policies and multi-factor authentication, will further reduce risk. Finally, conducting regular security assessments and penetration testing focused on path traversal and file access controls can help identify residual weaknesses.