CVE-2025-21490 is a vulnerability identified in the Oracle MySQL Server, specifically affecting the InnoDB storage engine component. It impacts multiple supported versions, including 8.0.40 and prior, 8.4.3 and prior, and 9.1.0 and prior. The flaw allows an attacker with high privileges and network access via multiple protocols to induce a hang or repeated crash of the MySQL Server, resulting in a complete denial-of-service (DoS) condition. The vulnerability does not compromise confidentiality or integrity but solely affects availability. The CVSS 3.1 base score is 4.9, reflecting a medium severity level, with the vector indicating network attack vector (AV:N), low attack complexity (AC:L), required privileges at high level (PR:H), no user interaction (UI:N), unchanged scope (S:U), and impact limited to availability (A:H). The underlying weakness is categorized under CWE-770, which relates to allocation of resources without proper limits or management, leading to exhaustion or deadlock scenarios. No public exploits have been reported to date, but the vulnerability is considered easily exploitable by attackers who already have high-level access to the network. The absence of patches at the time of reporting necessitates vigilance and proactive mitigation. This vulnerability is significant for environments where MySQL Server uptime is critical, as successful exploitation can disrupt database availability and impact dependent applications and services.

For European organizations, the primary impact of CVE-2025-21490 is the potential for denial-of-service attacks against MySQL Server instances, leading to service outages and operational disruptions. Industries heavily reliant on MySQL for transactional databases, such as banking, telecommunications, e-commerce, and public sector services, could experience interruptions affecting customer service, financial transactions, and data processing workflows. Although the vulnerability does not allow data theft or modification, the loss of availability can cause reputational damage, regulatory compliance issues (especially under GDPR if service disruptions affect data processing), and financial losses due to downtime. Organizations with distributed MySQL deployments or those exposed to network access by high privileged users are at increased risk. The lack of known exploits reduces immediate threat but also means organizations must be proactive in patching and monitoring. The impact is heightened in environments where high availability and continuous uptime are mandated, such as critical infrastructure and cloud service providers operating in Europe.

1. Monitor Oracle’s official channels closely for the release of security patches addressing CVE-2025-21490 and apply them promptly once available. 2. Restrict network access to MySQL Server instances by implementing strict firewall rules and network segmentation, limiting connections to trusted hosts and administrative users only. 3. Enforce the principle of least privilege by ensuring that only necessary users have high-level privileges required to exploit this vulnerability. 4. Implement robust monitoring and alerting for unusual MySQL Server behavior, such as frequent crashes, hangs, or resource exhaustion symptoms, to enable rapid incident response. 5. Consider deploying MySQL high availability solutions (e.g., clustering, replication) to minimize service disruption impact in case of a DoS event. 6. Conduct regular security audits and vulnerability assessments focusing on database servers and their access controls. 7. Educate system administrators and DBAs about this vulnerability and the importance of limiting privileged network access. 8. If possible, temporarily disable or restrict protocols that provide network access to MySQL Server until patches are applied, especially in environments where high privileged users are network accessible.