CVE-2025-6709 is a high-severity denial of service (DoS) vulnerability in MongoDB Server, identified as an improper input validation issue (CWE-20). The vulnerability arises from the server's improper handling of specific date values within JSON input when using OpenID Connect (OIDC) authentication. An attacker can exploit this flaw by sending a crafted malicious JSON payload via the mongo shell, triggering an invariant failure that causes the MongoDB server process to crash. This results in a denial of service condition, disrupting database availability. The vulnerability affects MongoDB Server versions 7.0 prior to 7.0.17, 8.0 prior to 8.0.5, and 6.0 prior to 6.0.21. Notably, for versions 7.0 and 8.0, exploitation does not require authentication, making the attack vector network accessible and easier to exploit remotely. For version 6.0, however, the attacker must be authenticated to induce the DoS. The CVSS v3.1 base score is 7.5, reflecting a high severity due to network attack vector, low attack complexity, no privileges or user interaction required (except for 6.0), and impact limited to availability (no confidentiality or integrity impact). There are no known exploits in the wild at the time of publication, and no official patch links were provided in the source data, indicating that remediation may require upgrading to fixed versions 7.0.17, 8.0.5, or 6.0.21. This vulnerability highlights the risks of improper input validation in complex authentication flows like OIDC, which can be leveraged to disrupt critical database services.

For European organizations, the impact of this vulnerability can be significant, especially for those relying on MongoDB Server for critical applications and services. A successful DoS attack can cause downtime, interrupting business operations, degrading service availability, and potentially leading to financial losses and reputational damage. Industries such as finance, healthcare, e-commerce, and public sector entities that depend on continuous database availability are particularly at risk. Since versions 7.0 and 8.0 can be exploited without authentication, attackers can remotely trigger outages without prior access, increasing the threat surface. The requirement for authentication in version 6.0 somewhat limits exploitation but still poses a risk from insider threats or compromised credentials. Additionally, disruption of MongoDB services may impact compliance with European data protection regulations (e.g., GDPR) if service interruptions affect data availability or processing obligations. The lack of known exploits currently suggests a window for proactive mitigation before widespread attacks occur.

European organizations should prioritize upgrading MongoDB Server to the fixed versions: 7.0.17 or later for the 7.0 branch, 8.0.5 or later for the 8.0 branch, and 6.0.21 or later for the 6.0 branch. If immediate upgrade is not feasible, organizations should implement network-level controls to restrict access to MongoDB instances, especially from untrusted networks, to reduce exposure. Enforce strict authentication and authorization policies, particularly for version 6.0 deployments, to limit potential attackers. Monitoring and alerting on unusual JSON payloads or OIDC authentication attempts can help detect exploitation attempts. Additionally, organizations should review their OIDC configurations and input validation mechanisms to ensure robust sanitization of date and other JSON fields. Conducting penetration testing focused on authentication flows and input validation can identify residual weaknesses. Finally, maintain up-to-date backups and incident response plans to minimize operational impact in case of successful DoS attacks.