CVE-2025-21504 is a vulnerability identified in the Oracle MySQL Server's Optimizer component affecting multiple versions including 8.0.39 and prior, 8.4.2 and prior, and 9.0.1 and prior. The flaw allows an attacker with high privileges and network access to exploit multiple protocols to cause the MySQL Server to hang or crash repeatedly, resulting in a complete denial of service (DoS). The vulnerability does not compromise confidentiality or integrity but severely impacts availability. The CVSS 3.1 base score is 4.9, with metrics indicating network attack vector (AV:N), low attack complexity (AC:L), high privileges required (PR:H), no user interaction (UI:N), unchanged scope (S:U), and impact limited to availability (A:H). The root cause is linked to CWE-770, which relates to allocation of resources without limits or throttling, leading to resource exhaustion or deadlock conditions. No patches are currently linked, and no known exploits have been reported in the wild, but the vulnerability is considered easily exploitable by an attacker with the necessary privileges. This vulnerability could be leveraged in multi-protocol environments where MySQL servers are exposed to network access, potentially disrupting critical database services.

For European organizations, the primary impact of CVE-2025-21504 is the potential for denial of service on MySQL database servers, which could disrupt business-critical applications relying on these databases. This could lead to operational downtime, loss of productivity, and potential financial losses. Since the vulnerability requires high privileges, the risk is elevated in environments where administrative access is not tightly controlled or where internal threat actors or compromised accounts exist. The lack of confidentiality or integrity impact means data breaches or data manipulation are not direct concerns from this vulnerability alone. However, availability disruptions in sectors such as finance, healthcare, telecommunications, and government could have cascading effects on service delivery and compliance with regulatory requirements like GDPR. Organizations with MySQL servers exposed to multiple network protocols or insufficient network segmentation are at higher risk. The absence of known exploits reduces immediate threat but does not eliminate the risk of future exploitation.

1. Apply security patches from Oracle as soon as they become available to address CVE-2025-21504. 2. Restrict network access to MySQL servers by implementing strict firewall rules and network segmentation, limiting exposure to only trusted hosts and protocols. 3. Enforce the principle of least privilege by auditing and minimizing high-privileged accounts that can access MySQL servers remotely. 4. Monitor MySQL server logs and system performance metrics for signs of hangs, crashes, or unusual resource consumption that could indicate exploitation attempts. 5. Implement robust access controls and multi-factor authentication for administrative access to reduce the risk of credential compromise. 6. Consider deploying intrusion detection/prevention systems (IDS/IPS) tuned to detect anomalous MySQL traffic patterns. 7. Regularly review and update incident response plans to include scenarios involving database availability attacks. 8. Conduct internal security assessments and penetration testing focusing on MySQL server exposure and privilege management.