CVE-2025-56406 is a security vulnerability identified in the mcp-neo4j software version 0.3.0. The vulnerability arises from the SSE (Server-Sent Events) service component of the application. Attackers exploiting this flaw can potentially gain access to sensitive information or execute arbitrary commands on the affected system. The exact technical mechanism is not fully detailed, but the involvement of the SSE service suggests that the vulnerability could be related to improper input validation or insufficient access controls in the event streaming functionality. This could allow an attacker to inject malicious commands or extract data that should otherwise be protected. Since mcp-neo4j is a software that interfaces with Neo4j graph databases, the impact could extend to compromising the confidentiality and integrity of graph data, as well as potentially allowing attackers to execute commands on the host system, leading to broader system compromise. No CVSS score has been assigned yet, and there are no known exploits in the wild or available patches at the time of publication. The vulnerability was reserved in mid-August 2025 and published in early September 2025, indicating it is a recent discovery.

For European organizations using mcp-neo4j 0.3.0, this vulnerability poses a significant risk. The ability to execute arbitrary commands could lead to full system compromise, data breaches, and disruption of critical services relying on graph database functionalities. Sensitive information leakage could include proprietary business data, personally identifiable information (PII), or intellectual property stored within the Neo4j databases. This could result in regulatory non-compliance, especially under GDPR, leading to legal and financial penalties. Operationally, exploitation could disrupt business processes dependent on the affected systems, causing downtime and reputational damage. Given the lack of patches and known exploits, organizations may be vulnerable if they have not implemented compensating controls. The risk is heightened for sectors with critical infrastructure or sensitive data, such as finance, healthcare, and government agencies within Europe.

Organizations should immediately conduct an inventory to identify any deployments of mcp-neo4j version 0.3.0. Until a patch is available, it is advisable to restrict access to the SSE service to trusted internal networks only, using network segmentation and firewall rules. Implement strict input validation and monitoring on the SSE endpoints to detect anomalous requests. Employ application-layer firewalls or Web Application Firewalls (WAFs) with custom rules to block suspicious payloads targeting the SSE service. Regularly audit logs for unusual activity related to the SSE service. If feasible, consider disabling the SSE functionality temporarily to eliminate the attack surface. Engage with the vendor or open-source community for updates and patches. Additionally, apply the principle of least privilege to the service accounts running mcp-neo4j to limit the impact of potential command execution. Finally, prepare incident response plans to quickly address any exploitation attempts.