CVE-2025-56406 is a high-severity vulnerability identified in the mcp-neo4j 0.3.0 software component. This vulnerability arises from the Server-Sent Events (SSE) service within the MCP server, which allows attackers to either obtain sensitive information or execute arbitrary commands remotely. The root cause involves insufficient access control (CWE-284), improper neutralization of special elements used in a command (CWE-77), and exposure of sensitive information to unauthorized actors (CWE-200). Notably, the MCP server does not enforce mandatory authentication by design, as it is intended for local environment use where authentication is presumed unnecessary. However, this design choice significantly increases the attack surface if the MCP server is exposed beyond a trusted local network. The supplier provides middleware solutions to isolate the MCP server from external access, but the absence of enforced authentication means that if an attacker gains network access to the MCP server, they can exploit the SSE service to execute arbitrary commands or extract sensitive data. The CVSS v3.1 base score is 7.5, reflecting a network attack vector with low complexity, no privileges required, no user interaction, and a high impact on confidentiality, but no impact on integrity or availability. There are no known exploits in the wild at this time, and no patches have been publicly released. This vulnerability highlights the risk of relying solely on network isolation without robust authentication and access controls, especially in environments where network boundaries may be porous or misconfigured.

For European organizations, the impact of CVE-2025-56406 could be significant, particularly for those using mcp-neo4j in development, testing, or local environments that may inadvertently expose the MCP server to broader networks. Successful exploitation could lead to unauthorized disclosure of sensitive information, potentially including intellectual property, internal configurations, or user data. Additionally, the ability to execute arbitrary commands remotely could allow attackers to pivot within the network, escalate privileges, or deploy further malware, undermining system integrity and organizational security. Given the lack of mandatory authentication, even internal threats or lateral movement by attackers who have gained initial access could exploit this vulnerability. The absence of impact on availability reduces the likelihood of direct denial-of-service consequences, but the confidentiality breach and command execution capabilities pose a serious risk to data protection compliance under GDPR and other European data privacy regulations. Organizations in sectors with stringent data protection requirements, such as finance, healthcare, and critical infrastructure, may face regulatory and reputational damage if exploited.

European organizations should implement the following specific mitigations: 1) Immediately verify the network exposure of MCP servers running mcp-neo4j 0.3.0 and ensure they are strictly isolated within trusted local environments with no external network access. 2) Deploy network-level controls such as firewalls and VLAN segmentation to restrict access to MCP servers only to authorized hosts and administrators. 3) Utilize the supplier-provided middleware or equivalent proxy solutions to enforce authentication and access control, effectively isolating the MCP server from untrusted networks. 4) Monitor network traffic and logs for unusual SSE service activity that could indicate exploitation attempts. 5) If feasible, consider disabling the SSE service or restricting its functionality until a patch or updated version with enforced authentication is available. 6) Engage with the supplier for updates or patches and plan for timely application once released. 7) Conduct internal audits to identify any MCP server deployments and assess their exposure and configuration against best security practices. These steps go beyond generic advice by focusing on network isolation, access control enforcement, and active monitoring tailored to the specific architecture and threat vector of this vulnerability.