CVE-2025-21500 is a vulnerability identified in the Oracle MySQL Server product, specifically within the Server Optimizer 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 with low privileges and network access through multiple protocols to exploit the vulnerability to cause the MySQL Server to hang or crash repeatedly, resulting in a complete denial-of-service (DoS) condition. The vulnerability does not allow unauthorized access to data (no confidentiality or integrity impact) but severely impacts availability. The attack vector is network-based with low attack complexity and does not require user interaction. The attacker must have low privileges on the network, which could be achieved via compromised credentials or insider threat. The vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling), indicating that the server fails to properly manage resource consumption under certain conditions triggered by the attacker. No patches or exploits are currently publicly available, but the vulnerability is considered easily exploitable once patches or proof-of-concept code emerge. The CVSS 3.1 score of 6.5 reflects a medium severity primarily due to the high availability impact and ease of exploitation. This vulnerability poses a risk to any organization running affected MySQL Server versions, especially those exposing MySQL services over the network without adequate access controls.

For European organizations, this vulnerability could lead to significant service disruptions, especially for enterprises relying heavily on MySQL Server for critical applications and databases. The denial-of-service condition could cause downtime, impacting business continuity, customer-facing services, and internal operations. Industries such as finance, telecommunications, healthcare, and e-commerce, which often use MySQL for backend data storage, could experience operational interruptions. The lack of impact on confidentiality and integrity reduces the risk of data breaches but does not mitigate the operational risk posed by service unavailability. Organizations with MySQL servers exposed to untrusted networks or with weak network segmentation are at higher risk. Additionally, the requirement for low privileges means that attackers with limited access, such as compromised internal users or attackers who have gained limited network foothold, could exploit this vulnerability. This could also affect cloud-hosted MySQL instances if network access controls are insufficient. The absence of known exploits in the wild currently lowers immediate risk but organizations should prepare for potential exploitation attempts once exploit code becomes available.

1. Monitor Oracle’s official channels for patches addressing CVE-2025-21500 and apply them promptly once released. 2. Restrict network access to MySQL Server instances by implementing strict firewall rules, allowing only trusted hosts and networks to connect. 3. Employ network segmentation to isolate database servers from general user networks and the internet. 4. Enforce strong authentication and access controls to minimize the risk of low privileged attackers gaining network access. 5. Regularly audit MySQL server configurations to ensure no unnecessary protocols or services are exposed. 6. Implement resource usage monitoring and alerting on MySQL servers to detect unusual activity that could indicate exploitation attempts. 7. Consider deploying Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) that can detect and block suspicious traffic patterns targeting MySQL services. 8. Prepare incident response plans to quickly address potential DoS attacks affecting database availability. 9. For cloud environments, use security groups and network ACLs to tightly control access to MySQL instances. 10. Educate internal teams about the risks and signs of exploitation to enhance early detection and response.