CVE-2025-21491 is a vulnerability identified in Oracle's MySQL Server, specifically within the InnoDB storage engine component. It affects multiple supported versions including 8.0.40 and earlier, 8.4.3 and earlier, and 9.1.0 and earlier. The flaw allows an attacker who already possesses high-level privileges and network access through multiple supported protocols to exploit the vulnerability to cause the MySQL Server to hang or crash repeatedly, resulting in a denial of service (DoS) condition. The vulnerability is classified under CWE-770, which relates to the improper management of resources, leading to exhaustion or deadlock scenarios. The CVSS 3.1 base score is 4.9, indicating a medium severity primarily due to its impact on availability without affecting confidentiality or integrity. The attack vector is network-based with low complexity, but requires high privileges and no user interaction. No public exploits have been reported yet, and no patches are currently linked, suggesting that organizations should monitor Oracle advisories closely. The vulnerability could disrupt database availability, impacting applications and services dependent on MySQL Server for data storage and retrieval.

For European organizations, the primary impact of CVE-2025-21491 is the potential for denial of service against critical database infrastructure running MySQL Server. This could lead to downtime of business-critical applications, loss of productivity, and potential financial losses. Sectors such as finance, telecommunications, government, and e-commerce that rely heavily on MySQL for backend data management are particularly at risk. Availability disruptions could also affect customer-facing services, damaging reputation and trust. Since the vulnerability requires high privileges, the risk is somewhat mitigated by existing access controls; however, insider threats or compromised administrative accounts could exploit this vulnerability. The lack of impact on confidentiality or integrity reduces the risk of data breaches but does not eliminate operational risks. Organizations with distributed MySQL deployments or those using multi-protocol access are more exposed. The absence of known exploits currently provides a window for proactive mitigation.

1. Monitor Oracle's official security advisories and apply patches or updates as soon as they become available to address CVE-2025-21491. 2. Restrict network access to MySQL Server instances using firewalls and network segmentation, limiting exposure to trusted hosts and administrative networks only. 3. Enforce strict access controls and least privilege principles to minimize the number of users with high privileges capable of exploiting this vulnerability. 4. Implement robust monitoring and alerting for unusual MySQL Server behavior, such as frequent crashes or hangs, to enable rapid detection and response. 5. Consider deploying MySQL Server in high-availability configurations with failover capabilities to reduce downtime impact. 6. Regularly audit and review user privileges and network access policies to ensure compliance with security best practices. 7. Use encrypted connections and secure authentication mechanisms to reduce risk of privilege escalation. 8. Conduct internal penetration testing and vulnerability scanning focused on MySQL Server to identify potential exploitation paths.