CVE-2025-21555 is a vulnerability identified in Oracle MySQL Server, specifically within the InnoDB storage engine component. It affects 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 exploit the vulnerability without user interaction. The attacker can cause the MySQL Server to hang or crash repeatedly, resulting in a complete denial of service (DoS). Additionally, the attacker can perform unauthorized data manipulation operations such as update, insert, or delete on data accessible by the MySQL Server. The CVSS 3.1 base score is 5.5, indicating a medium severity, with the vector string CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:H. This means the attack requires network access, low attack complexity, and high privileges but no user interaction, impacting integrity and availability but not confidentiality. The vulnerability is categorized under CWE-863, which involves improper authorization. No patches were linked at the time of reporting, and no known exploits in the wild have been documented. The vulnerability poses a risk primarily to environments where MySQL Server is exposed to high privilege users over the network, potentially allowing disruption of database services and unauthorized data modification.

For European organizations, the impact of CVE-2025-21555 can be significant, particularly for those relying on MySQL Server for critical business applications and data storage. The ability of an attacker to cause a denial of service by crashing or hanging the database server can lead to operational downtime, affecting service availability and business continuity. Unauthorized data modification capabilities threaten data integrity, potentially leading to corrupted records, inaccurate business decisions, and compliance violations, especially under GDPR where data integrity is crucial. Although confidentiality is not directly impacted, the integrity and availability issues can indirectly affect trust and regulatory compliance. Sectors such as finance, healthcare, telecommunications, and public administration, which often use MySQL databases and require high availability and data accuracy, are particularly vulnerable. The requirement for high privileges limits the attack surface but does not eliminate risk, especially in environments where privileged credentials may be compromised or misused. The lack of current known exploits reduces immediate risk but underscores the need for proactive mitigation.

1. Apply official Oracle patches promptly once they are released to address CVE-2025-21555. 2. Restrict network access to MySQL Server instances by implementing strict firewall rules and network segmentation, limiting access to trusted hosts and administrators only. 3. Enforce the principle of least privilege by auditing and minimizing high privilege accounts that have network access to MySQL. 4. Implement strong authentication and access controls for MySQL users to reduce the risk of privilege escalation or misuse. 5. Monitor MySQL server logs and network traffic for unusual activity indicative of exploitation attempts, such as repeated crashes or unauthorized data modification commands. 6. Consider deploying database activity monitoring (DAM) solutions to detect and alert on suspicious operations. 7. Regularly back up databases and test restoration procedures to mitigate the impact of potential data corruption or service disruption. 8. Educate database administrators and security teams about this vulnerability and ensure incident response plans include scenarios involving database DoS and data integrity attacks.