CVE-2026-21929 is a vulnerability identified in Oracle MySQL Server versions 9.0.0 through 9.5.0, specifically within the server's parser component. The flaw allows an attacker with low privileges and network access through multiple protocols to cause the MySQL Server to hang or crash repeatedly, resulting in a complete denial of service (DoS). The vulnerability does not allow unauthorized disclosure or modification of data, focusing solely on availability disruption. The CVSS 3.1 base score of 5.3 reflects a medium severity, with the vector indicating network attack vector (AV:N), high attack complexity (AC:H), low privileges required (PR:L), no user interaction (UI:N), unchanged scope (S:U), and impact limited to availability (A:H). Exploiting this vulnerability is considered difficult due to the high complexity, but it does not require user interaction, making automated or remote attacks feasible if network access is available. No known exploits have been reported in the wild, suggesting limited active exploitation at this time. The vulnerability affects multiple network protocols that MySQL Server supports, increasing the potential attack surface. The parser component is critical for interpreting SQL queries, and its compromise can destabilize the server process. This vulnerability underscores the importance of securing MySQL Server instances, especially those exposed to untrusted networks.

For European organizations, the primary impact of CVE-2026-21929 is the potential for denial of service attacks against MySQL Server instances. This can disrupt business-critical applications relying on MySQL databases, leading to downtime, loss of productivity, and potential financial losses. Organizations in sectors such as finance, telecommunications, e-commerce, and public services that depend heavily on database availability are particularly at risk. The inability to maintain database availability could also affect customer trust and regulatory compliance, especially under GDPR where service continuity is important. Since the vulnerability does not allow data breaches or integrity compromise, the impact is limited to availability. However, repeated or prolonged outages could indirectly affect data integrity if recovery processes are not properly managed. The difficulty of exploitation reduces the likelihood of widespread attacks but does not eliminate the risk, especially from skilled attackers targeting specific organizations.

1. Apply official patches or updates from Oracle as soon as they become available to address this vulnerability. 2. Restrict network access to MySQL Server instances by implementing strict firewall rules, allowing only trusted hosts and networks to connect. 3. Disable or limit exposure of MySQL protocols and services that are not required, reducing the attack surface. 4. Monitor MySQL Server logs and system behavior for signs of unusual hangs or crashes that could indicate exploitation attempts. 5. Implement network segmentation to isolate database servers from less secure network zones. 6. Use intrusion detection and prevention systems (IDS/IPS) to detect anomalous traffic patterns targeting MySQL services. 7. Regularly review and minimize user privileges on MySQL to reduce the potential impact of compromised accounts. 8. Conduct periodic security assessments and penetration tests focusing on database infrastructure to identify and remediate weaknesses.